Art. XXVIII.—Notes on the Physiology and Anatomy of the Tuatara (Sphenodon güntheri).

By A. K. Newman, M.B., M.R.C.P.

The dark form is found in the North; the intermediate at East Cape Island; and the lightest form in the South.

Sphenodon punctatum was the form so elaborately described by Dr. Günther. The other species has not been anatomically examined.

Classification of Sphenodon.

At present the position of the Sphenodon in the Sauropsida is not yet quite certainly known. To meet the difficulty Dr. Günther proposes the following division of recent Reptilia:—

I. Squamata. II. Loucata. III. Cataphracta.

He divides the Squamata into Ophidia, Lacertilia, Rhynchocephalia. If external characters alone were considered, he says it would most resemble Ayamidœ, of which genus Professor Peters thinks it merely an aberrant form. Professor Seeley talks of Lacertia, Rhynchocephalia, and Crocodilia. In his “Forms of Life,” Rolleston talks of it as a “low lizard.”

Huxley divides the Lacertilia into various groups:—I. Pterygoid and quadrate bones united. II. Pterygoid and quadrate bones disunited. Class I. he divides into A., a columella and inter-orbital septum; and subdivides it into those with amphicœlous and those with procœlous vertebræ—Kionocrania amphicœlous and Kionocrania procelor. Those with amphicœlous vertebræ are again divided into Acrodont or Pleurodont, and Thecodont. There are three Orders: Acrodont or Pleurodont Acalabota, Rhynchocephalia, and Homeosauria.

Relationship with extinct Reptilia.

So far as is yet known the relationship between the Sphenodon and extinct reptiles is of great interest. Lyell writes:^*—The Hyderapedon was afterwards discovered in beds of about the same age (upper trias or keuper) in the neighbourhood of Warwick and also in South Devon, and remains of the same genus have been found in Central Italy and Southern Africa, in rocks believed to be of triassic age. It has been shown by Professor Huxley to be allied to the living Sphenodon of New Zealand. The recent discovery of a living saurian in New Zealand so closely allied to this supposed extinct division of the Lacertilia seems to afford an illustration of a principle pointed out by Mr. Darwin of the survival in insulated tracts, after many changes in physical geography, of orders of which the congeners have become extinct on continents where they have been exposed to the severer competition of a larger progressive fauna.” Professor Huxley also discovered that the extinct lizards of the triassic age, viz., Rhynchosaurus and the Hyderapedon, were both closely allied to this Sphenodon. Still more recently, in Illinois, certain fossil reptilia have been found which possess a feature common alike to the Archegosaurus, stegocephalic batra-

chians and the Sphenodon, viz., a longitudinal axial perforation of the vertebræ.

Professor Seeley, in a series of most elaborate essays, compares the bones of many living and extinct reptiles with each other. He finds that “The abdominal ribs of Hatteria are like those of Plesiosaurus, and in one species (for two species seem to me to be figured by Dr. Günther) the medium V-shaped bone is overlapped by a splice from a bone external to it. In another species this is replaced by a joint, and the external piece has a squamous expansion on the middle of its anterior and posterior margin, unlike anything seen in Plesiosaurus. But, as in Plesiosaurus, other bones are introduced between these elements, so as to make the abdominal ribs nearly twice as many as the costal ribs.”^* He compares Ichthyosaurus and Sphenodon thus:—“The apparatus of infracostal ribs seems capable of being moved away with equal entirety in both groups, owing to the union of some of the elements by overlap.”^† Günther thinks it most like the Rhynchosaurus of the new red sandstone of Shropshire.

Habitat.

Until the last few years tuataras abounded in certain parts of the South Island, especially on the banks of the Waimakariri river. About thirty years ago four were caught on Mount Victoria, near Wellington; one on Somes Island in Wellington harbour; and two by Mr. Mason, in the Hutt Valley; and in 1864 several were caught at Makara. They frequent the sandy banks of rivers, and hide beneath fallen trees. They abound on the Rurima Rocks, and on other islets in or near the Bay of Plenty, on Motiti, and East Cape Island. Many were found on the Brothers Rocks in Cook Strait during the recent erection of the lighthouse, but are now almost, if not quite, exterminated by curiosity-hunters. On the large islands none exist. Bush fires, wild pigs, dogs and cats, reptile-eating Maori tribes, and the advance of civilization have swept away all of these strange creatures, except the few which infest the tops of inaccessible rocky islets. Only one of the islets forming the Brothers group, in Cook Strait, was inhabited by them: this one was covered with loose sand and shingle, in which the tuatara burrowed holes. The other two uninhabited islets are merely bare hard rocks, affording neither food nor shelter.

Habits.

Tuataras grow very slowly; young specimens have apparently not increased in size during a whole year. A full-grown specimen must be many years old. One is known to have lived out two generations of men. Tuataras, like most reptiles, are very sluggish in their habits. They sleep during the greater part of the day, coming out of their holes at night for

behind them, just as a dog does when scratching out a rat-hole. Günther objects to the belief that they burrowed, because he says their fore-limbs are slender; but the skeletons in the Colonial Museum show that they are not very slender, and are certainly strong enough and stout enough to be used for burrowing in loose soil. The long sharp claws too are admirably adapted for penetrating deep into loose sand or light loam. The claws are sharply carved out on their posterior aspects. They soon become blunted when used against the wooden or tin walls of a cage. The dorsal spines are no hindrance when entering holes, because they are very soft, being easily bent on themselves or pressed down on one or other side.

Locomotion.

Dr. Günther elaborately described the abdominal ribs, and, speculating on their use, inferred that their special function was “to assist in locomotion.” He thought that by being approximated these ribs would assist the animal in crawling over rocks, especially as to each of the ribs (twenty-five or twenty-six in number) was attached a row of scales, the ends of which, he thought, were tilted up, thus causing a roughened abdominal surface, which would also help the animal. When dissecting a tuatara, it seemed to me that the amount of approximation between the ribs must be infinitesimal, and therefore these ribs could not be subservient to the special function of assisting in locomotion. I therefore carefully studied the motions of living tuataras, to ascertain which view was correct.

Tuataras are very lazy in all their movements, and even when frightened they move very slowly. Their usual pace is a very slow crawl, the abdomen and tail trailing on the ground. The femora are articulated at right-angles with the pelvis, and the tibiæ and fibiæ at right-angles to the femora; this mode of articulation causes a great strain on the muscles of the posterior limbs, therefore when at rest the trunk rests on the ground. I tried many experiments with mine and narrowly watched their movements. When driven fast, or when chasing prey, they always lift the whole trunk off the ground, it does not touch at any spot. This rapid gait is very “wobbling,” something like a man swimming sideways. After running three or four yards they grow weary and stop. They cannot jump the smallest obstacle, their limbs being too feeble. In ordinary crawling they propel themselves by means of their limbs alone, and the abdominal ribs take no part in these movements, though trunk and tail rest on the ground. The abdominal ribs are not used during either slow or rapid movements, the limbs doing all the work; the limbs are quite strong enough to drag the body and tail along the ground, and during more rapid but very brief movements are powerful enough to lift the body and great part of the long heavy tail off the ground.

If a tuatara be lying with its abdomen across the edge of a plate

or the ridge of a stone it cannot wriggle itself off unless it uses its limbs. The trunk is short and these twenty-five or more ribs are very close together, the limbs not being far apart; they are bound together by large quantities of strong fibrous tissue, the amount of movement between each rib is very small, and when lifted off the ground and twisting its body about, the ventral plates do not have their roughened posterior edges tilted up by approximation of these ribs. I think that the abdominal ribs play no part in locomotion; whether the reptile crawls or runs or climbs up rocks the ribs are powerless, and afford the limbs no help. I am of opinion that the ribs are useful not to assist the limbs, but to act as a broad, strong, abdominal sole. Any one who has dissected a female tuatara with its eggs filling the whole abdomen, and has noticed the enormous size of these eggs, would be convinced that the abdominal ribs would be of the greatest use to the animal by supporting and protecting them from injury. A tuatara carries ten large eggs, all about the same size and weight, any two of these weigh as much as the whole of the other thoracic abdominal and pelvic viscera. These eggs lie in two parallel rows, extending from the cloaca, almost to the farther end of the thorax, they lie on these ribs, which support them, for the ligaments which attach the oviducts to the spine are thin and long. By this means the unusual weight is well distributed over the body. When crawling over the edges of sharp stones the ribs would protect the eggs and other viscera; with the true ribs and vertebræ they form a strong, compact and yet mobile case.

Günther also says the sharp claws “show that in a normal state they cannot be much used in dragging the heavy body or even in burrowing,” but this is a statement founded on a misconception of their mode of progression. The tuatara walks on its pes and manus and not on its digits and claws. It is plantigrade not digitigrade, as indeed might easily be learnt from examination of the skin and its scales which cover those parts. When the animal is at rest the long nails keep the digits off the ground, and almost all the pressure of the limbs is on the pes and manus; the abdomen and tail rest on the ground wholly unsupported by the limbs.

Tail fracture and reproduction.

Of great interest is the subject of tail reproduction in tuataras. Professor Huxley says that “In many Lacertilia (Lacertœ iguanœ geckos) the caudal vertebræ have a very singular structure, the middle of each being traversed by a thin unossified transverse septum. The vertebra usuall breaks with readiness through the plane of the septum, and when such lizards are seized by the tail that appendage is pretty certain to part at those weak points.” Knox discovered that this curious feature obtained in the tuatara; he also learnt that the injured part will heal, but distinct

joint itself is covered with much thinner skin and less tough tissue, and it is at a joint that the tail breaks. The tail bends only at the joints, the inter-spaces being rigid. The new tail is smooth, has no joints, is composed internally of cartilage, “like that of the lowest fishes,” and by its external appearance can be at once distinguished from the older portion. In support of Knox's belief that owing to the dragging away of the medulla spinalis the tail would not be reproduced, I may cite the fact that experiments have shown that certain lizards which reproduce their tails will not do so if a red-hot wire be passed some distance up the vertebral canal thereby destroying the core.

The tail may be fractured at almost any point; if at a distant point the animal soon recovers, but if near the pelvis it very frequently dies. In my full-grown tuatara the tail broke between the vertebræ; repair began by rounding of the broken end with compaction of cicatricial tissue. No scales were formed on the new part or new vertebræ in it.

Abdominal ribs.

In addition to a number of vertebral ribs, the tuatara has twenty-five or twenty-six (Günther) abdominal ribs (Knox's had twenty-five, mine twenty-five). They are double the number of the spinal ribs. To about the middle of each abdominal rib the spinal rib is attached, thus +, forming a broad flat sole to support the viscera internally, and externally to protect it from injury. Günther considers “this system of bones is similar to but essentially different from that observed in crocodiles and some lizards (Chameleon, Polychrus, etc.), known as abdominal ribs or abdominal sternum, and considered to be the ossified inscriptiones tendinæ of the abdominal muscles.” Günther also says, that “in no saurian, so far as we know at present, have they any relation to the external integuments.” Knox thought they were dermal, and Rolleston calls them “parostotic ossifications of the subcutaneous fibrous mesh.” This opinion must be incorrect, for they lie imbedded in the rectus abdominis muscle. An examination of skeletons will incontestably prove that they are not dermal or exoskeletal but endoskeletal.

Tuataras breathe slowly. As the abdomen and thorax are tightly bound in by abdominal ribs, the abdomen and thorax do not change their form, the vertebral ribs alone moving during respiration. If a tuatara be watched while breathing, it will be seen that the greatest amount of motion is at the junction of the vertebral and abdominal ribs. The lungs (merely thin bags) run nearly the whole length of the thoracic and abdominal cavities. The tuatara inspires, its throat swells largely, then the capacious lungs. The walls of the trunk are then motionless for many seconds, sometimes upwards of half-a-minute, ere expiration occurs. Owing to the peculiar shape of the

skull, with its two bars and additional bones, the pharyngeal cavity is enormously enlarged. When the tuatara inspires it greatly depresses the hyoid and trachea, thereby still more enlarging the pharyngeal cavity. By this means the tuatara inhales a large quantity of air, filling the lungs, mouth, trachea, and the large pharyngeal cavity. This peculiar mode of respiring by depressing the hyoid bone (which with its cornea is very large) enables the tuatara to inhale sufficient air to allow it to remain under water for hours without coming to the surface to breathe. The quantity of air in the lungs, trachea, mouth, and distended pharynx amounts to several cubic inches, which is sufficient to sustain life for some time in a small and cold-blooded reptile.

Tuataras swim freely—sometimes with only the nostrils above water, at others swimming as freely and well under it. As tuataras are found usually on isles, or on the banks of rivers, it may be that they find part of their food in the water. The Ichthyosaurus and Plesiosaurus marine reptilia had abdominal ribs, and the former amphicœlian vertebræ like the Sphenodon.

Dissection of Female Tuataras.

Total length, 16 inches, of which 8.¾ inches were tail. Dorsal spines beginning at the occiput stretch along the back to the end of the tail; between the scapulæ five or six are wanting, and about three over the sacrum. Those on the neck and trunk are flattened laterally, blade-like, and acuminated; they are quite soft, and many are not erect. The caudal spines are attached one to each section of the verticellated tail. About the middle of the tail, instead of being flattened laterally they are prismoidal, being much wider at the base and not so sharp. As the tail sections dwindle so also do the spines till they can scarcely be said to exist. This tuatara has ten cervical spines, then an interval between the shoulders, then fifteen dorsal, an interval over the sacrum, and forty-one caudal spines. In Lophocalotes interruptus the spines, as in Sphenodon, reach from the head to end of tail, and are also interrupted between the scapula and over the sacrum. So also in Tiaris tuberculata; in this lizard there is on each side a row of secondary spines. In Sphenodon, as in certain other lizards where the spines are absent between the scapulæ, their place is occupied by a large black patch of skin; some spines are also black. The skin of Sphenodon is marked by several ridges which reach from head to tail, running parallel with the dorsal crest. One ridge extends along the trunk from the fore to the hind limbs; it is due to the free projecting ends of the abdominal ribs.

Two ridges beginning at the end of the rounded snout run backwards above the nasal openings and the eyes, giving a triangular look and a flat appearance to the form of the head. In many places the epithelial cells are accumulated, forming small spines which irregularly crown some of these skin ridges.

At the under surface of the jaw are small white scales, some partially others fully formed; they partially overlap each other, as do shingles on a house roof. At the throat they are more largely and fully developed, and are of irregular shape, usually with many straight sides and rounded edges. Gradually these scales become arranged in parallel rows, the posterior edge of the front row overlapping the anterior edges of back ridge. On the abdomen these plates are much larger and more regular in shape (parallelograms) and are arranged in rows, each row being closely bound by its anterior edge to an abdominal rib. About an inch from the transverse vent they become smaller, more irregular in shape, and the ends of the rows bend round, so that at the vent the rows are indistinct. Behind the vent they are small, but soon grow larger, and then rows of straight-sided plates almost encircle the tail. These tail plates are longer and narrower, though as regularly placed as those on the abdomen. Under the throat the skin hangs in loose irregular folds.

No sign of ears. Nostrils, two small holes almost hidden by lateral cranial skin ridges. These holes look upwards. A needle passed into them passes downwards and forwards—not backwards.

Mouth 1.2 inches long, quite straight.

Fore limbs shorter than the hind ones. Pes and manus have each five digits armed with sharp nails, curved like the teeth of a rodent. Pollux short and thick. Hallux slender and widely separated from other digits. Both pes and manus are large and covered on the under surface with small white scales.

To the exhaustive description of the abdominal ribs given by Günther I cannot add anything, except a remark on a peculiarity which he noticed in one specimen. He examined six specimens and in one he found “a very curious anomaly as regards the union of the three bones of which the abdominal ribs consist; they were united by joints.” This peculiarity existed only in the alternate ribs. This did not obtain in either of my specimens, which belonged to a different species. It is therefore probably a variation, and not a mark of a distinct species.

Dentition.

Dr. Günther described specimens in all of which there were in each premaxillary bone a pair of incisors, far larger than any of the other teeth. These teeth were confluent at the base, and in old specimens when the cones were worn down, the incisor appeared as if a single tooth, resembling a rodent's incisor. Dr. Knox, however, found that in one of his two specimens there were in each premaxilla three teeth, all confluent at the base; the other specimen had but two cones. This newly discovered cone is nearer the middle line than the others. It is far smaller, slenderer, and sharper, and

would very soon be worn down. It looks like a mere rudiment. In one of my specimens (both from the Brothers) this third cone was present, in the other absent. The one in which it was absent was not, I think, an old specimen; its teeth are in good order and very little, if at all, worn. This therefore cannot be a specific distinction. Drs. Günther and Knox disagree in the number of teeth assigned to each maxilla and palate, but this arises from the fact that Dr. Knox considers several of them complex teeth, while Dr. Günther counts each cone as a distinct tooth. Günther says there are about eighteen teeth in each maxilla which Knox counts as six. I counted sixteen in mine and thirteen on each palate. Of the latter the largest and strongest were in the middle. The teeth of the maxilla press the food between the parallel rows of teeth, maxillary and palatine, and enter the groove between them. Thus the three sets of teeth are differently sharpened; the mandibular teeth have both inner and outer sides ground by the others, while the maxillary are sharpened on their inner and the palatine on their outer faces. The teeth in my specimens were thirteen in the palate, of which the anterior were very small. In the mandible nineteen, a canine and incisors, two in number, and confluent at the base. The teeth in mandible and maxilla near the incisors are very small, and are soon worn away or ground very small. In the other specimen was an additional incisor.

The muscles which move the lower jaw are very short, thick, and powerful. The crushing force of the jaws is very great.

The tongue is thick and rough, the glottis a long narrow slit, with closely-meeting raised edges. On forcibly opening the mouth of a living specimen the tonsils appear very large.

The posterior nares, two slits in the roof of the mouth, are situated just inside the maxillary teeth at the junction of maxillary and premaxillary bones.

Thorax, Abdomen, and Pelvis.

This large cavity is not divided by a diaphragm, though a portion of the peritoneum is attached to the ribs where a diaphragm might be expected. The peritoneum is a delicate membrane, in some parts colourless and transparent, in others darker. The peritoneum is almost black in and near the pelvis, but in many parts is much lighter, in some being of a greenish-brown tint. The peritoneum lines the whole of the trunk cavity, and gives off various large processes which attach the different organs to the spine; of these the largest are those which attach the rows of eggs to the spine. The processes attached to the oviducts are black, but the mysentery is transparent. The processes are half-an-inch in breadth, allowing the rows of eggs to rest on the abdominal walls. In the mysentery are long grey bodies, corpora adiposa.

The long straight trachea, whose rings only partially surround it, divides into two short bronchi, each of which ends in a large cavity. The lungs are two long thin sacs, with partly transparent walls. The walls have on their inner face a few villous-like projections. There is in each lung this one large cavity, therefore the bronchi do not divide or subdivide as in the higher animals. Each lung is one-and-three-quarter inches in length, each lies in close contact with the stomach. No thymus or thyroid.

Female Generative Organs.

In the first tuatara the whole of the abdomen and pelvis was filled with two parallel rows of eggs. There were five eggs in each row. All were about the same size, and appeared in the same stage of development. One was deep in the pelvis, and this seemed a trifle larger than the others. Its end too was sharper, and it was longer than the others: it was evidently being moulded ere being extruded, just as is the head of the human fœtus. These eggs were five-eighths of an inch in length, with their thin ends pointing towards the cloaca, and extended from the heart to the pelvis. They present a most curious appearance. All the other organs seemed squeezed and pushed aside by them. The space occupied by two eggs is equal to that occupied by the other abdominal viscera. The oviducts, firm white tubes, with constrictions dividing each egg from the others. Each oviduct is attached by a long, thin, black process of peritoneum to the spine; but this is long enough to allow the eggs to rest on the abdominal ribs.

In the space between these ligaments lies the spinal lobe of the liver. Each egg is covered with a thick dense membrane, composed of closely-interwoven bands of fibrous tissue, and lined by a thinner and smoother membrane. Each egg consisted of an oily-looking fluid, and lying in this a large dense yellow portion. In the eggs kept in spirits this portion was coagulated and granular. In the other specimen, where the eggs were far less developed, the dense internal portion alone was visible. The ovaries are two thin flattened bodies, attached by peritoneums to the ribs near the junction of abdomen and thorax. Each ovary contained great numbers of very small eggs, flattened by pressure against each other.

Bladder, large hollow viscus, extending half-an-inch above the pelvis, and opening into the cloaca. Günther says that the males have no “intromittent copulatory organ.” Most Lacertilians have a double or bifid penis; the geckos have none. On account of the absence of a penis and a membrana tympani, Professor Peters proposes to class them with Agamidœ. Dr. Günther's description of the anal scent-gland in the males applies exactly to the females.

Muscles of hind limbs.

Musculus agitator caudæ, also called ileoperoneal, very long and thin, arises from the sacrum, passing behind the posterior border of the ilium runs down the outer and posterior aspect of the leg, and is inserted by a tendinous expansion into the outer and upper part of the fibula. In its course it covers in the great ischiatic nerve from its escape behind the ilium till it pierces the gastrocnemius and soleus. It draws the limb backwards.

Extensor quadriceps cruris should be called triceps not quadriceps, for it arises by three heads. The long head arises from the whole of the outer surface of the ilium, occupying the space which in men is occupied by the glutæi; it grows bulky and passes down the outside of the thigh to join the other heads. The short head arises from the whole of the outside of the femur just below the insertion of the M. pectineus. The third head arises from the ilio-pubic suture, and near the knee joins the other heads, from which it is at first widely separated. The musculus pectineus divides the last two heads. The slender head arises close to the origins of the gracilis and sartorius. The three heads converge to be inserted by a very broad and strong fascia and ligament into the upper surface of the tibia. The ilio-pubic head draws the limb forward.

There is a muscle which Günther calls pectineus, but which Mivart and Sanders, in Menopoma, call psoas and iliacus. I think it should be called iliacus. Günther calls a wholly different muscle iliacus internus. I know not why, for it is an external muscle, corresponding in size to glutæus medius. A muscle arises from the inner surface of the cartilaginous edge of the uncinate process of the pubis, and passes on over the edge of the ilium, to be inserted into the fascia lata, in the same manner as the tensor vaginæ femoris. Below this small muscle is the one which Günther calls pectineus; it is large and springs from the whole of the ventral surface of the pubis and ilium, crosses the ilio-pubic crest, lies close to the acetabulum, and is inserted by a broad tendon into the middle-third of the outer surface of the femur. It also arises from the ilio-pubic ridge. It draws the leg forward and rotates it outwards: it is very powerful. This muscle and the preceding one are separated from the bladder and cloaca by peritoneum. In some lizards this muscle arises by four heads. In Platydactylus japonicus Sanders found the muscle which I have called tensor vaginæ femoris.

Musculus gracilis arises from the uncinate process of the pubis, anterior to origin of the long head of extensor cruris, runs down the inside of thigh alongside the head of the biceps, and is inserted into posterior and upper part of the tibia. It antagonizes the biceps.

A broad thick sheet of muscle arises from the symphysis ossium pubis et

M. iliacus (a muscle so called by Günther) arises from the whole of the ascending outer surface of the ilium, directly covers in the hip-joint, and is inserted by a broad fleshy band into the posterior and hinder aspect of the femur. Its origin is hidden by the long head of the extensor cruris, and is separated by the very strong fascia. This muscle resembles in position, origin, and insertion the glutæus in man.

Quadratus femoris arises from the border and side of the tuber ischii, and is inserted into the digital fossa. It is a small muscle, about one quarter the size of the obturator externus. Gemelli and pyriformis are represented by a small mass of muscle coming from the ventral surface and posterior edge of the vertical ilium, and inserted into the head of the femur just below the capsular ligament.

Acetabulum.

Length of cavity half as long again as the breadth; lower border straight, upper curved. Capsular ligament very strong, lined by synovial membrane. It embraces the edges of the acetabulum, and is especially thickened on the upper part by a ligament corresponding to the ligamentum teres in man. This ligament is inseparable from the capsule; the latter is also specially thick anteriorly. The acetabulum faces directly outwards and slightly backwards. Acetabulum shallow, very slight lip, dislocation would easily occur but for the cartilage round the edge, the capsular ligament, and the muscles which lie in contact with and materially strengthen it. The obturator foramen is long and oval, filled by a membrane, which is pierced by the obturator nerves and vessels.

Fascia.

Fascia lata of the thigh is attached to the pelvic rim and superior external border of the ischium; here it is strong and thick and covers the whole of the outer side of the thigh and ends in a broad aponeurosis which closely envelopes the knee joint. It receives the insertion of the tensor vaginæ femoris. The fascia is very intimately connected with the long head of the extensor cruris, much resembling relationship between the human glutæus maximus and fascia lata. A very strong fascia closely binds the caudal muscles.

The great ischiatic nerve passes out behind the ilium, gives off numerous branches and runs down the popliteal space, in the lower part of which it divides into several branches just prior to entering the sural muscles. It is covered in by the musculus agitator caudæ, to which it supplies a branch.

Muscles of fore limbs.

The deltoid arises from the posterior portion and border of the cartilaginous scapula and passes directly downwards to be inserted into the middle of outer side of humerus, its tendinous portion passing between the triceps

and coraco-brachialis. The supra-spinatus, teres and infra-spinatus form a broad mass arising from the scapula, and, still continuing a broad mass, pass over the shoulder joint to the outer and upper part of the humerus.

The serratus magnus arises from the fourth and fifth ribs, and from the hæmapophyses passes forward to the posterior border of the cartilaginous and bony part of the scapula. The more numerous and powerful fibres are inserted into the bony portion. The subscapularis large thick muscle takes its origin from the inner surface of the bony and cartilaginous scapula and is inserted into the humerus. No rhomboidei (Günther). The biceps brachii arises by one head from the scapula and humerus, by the other from the surface and margin of the cartilaginous coracoid; opposite the shoulder it narrows into a thin tendon, and over this the tendon of the pectoralis-major plays freely; becoming fleshy again it travels down the arm, its tendon of insertion piercing the flexor and extensor muscles of the fore-arm and reaching the ulna. The coraco-brachialis arises from the coracoid, and is inserted down the whole length of the humerus as far as the external condyle. A large flat muscle arises from the coracoid bone near its junction with the scapulæ and is inserted into the head of the humerus—epicoraco-humeral. In Iguana Mivart describes a similar muscle. The triceps arises by only two heads, one attached to the constricted part of the scapula, the other a long fleshy slip coracoid. They join, and forming one muscle are attached all down the posterior surface of the humerus and into the olecranon.

Throat muscles.

A broad strong sheet of fascia arising from the clavicle passes forward, covering in the under surface of the neck and becoming attached along the whole length of the inner surfaces of the mandibles, becoming much thinner near their junction, and is connected by loose cellular tissue with the deeper muscles. The mylo-hyoid is well developed; it stretches from mandible to mandible. The sterno-cleido-mastoid arises fleshy from the whole of the clavicle, passes forwards and upwards to be inserted into the mastoid and parietals. It may easily be divided into several portions looking like distinct muscles. By two heads the omo-hyoid arises, one from the outer end of clavicle, the other from the inner. In Iguana this muscle arises by one broad head. It wends inwards to the mesial line and passes upwards to be inserted into the laryngeal cartilage. It is separated by cellular tissue from its fellow-muscle, and internally is closely connected with the trachea. It is probably what in man is distinguished as sterno-thyroid and omo-hyoid. The genio-hyoid is a small muscle inserted with its fellow into the mandibles near their junction. The stylo-hyoid arises from the mastoid and ends in a remarkably long tendon, which curves round the posterior