Spiracular Arteries. (Fig. 2.)

These are often called the pseudobranchial arteries, but, as a pseudobranch is not always present, spiracular is perhaps the better term. In Typhlonarke the afferent spiracular artery (a.s.a.) passes median to the pseudohyal and lateral to the hyomandibular cartilage. Before reaching the spiracle, it gives off a branch (a.m.a.) which possibly represents the afferent mandibular artery, the mandibular arterial arch being interrupted in its lower half in all elasmobranchs except Squatina squatina and Callorhynchus antarcticus. This branch is also present in Torpedo and Raja, but as in Typhlonarke, there is no ventral connection. The efferent spiracular artery (e.s.a) is in Typhlonarke a very fine vessel which leaves the spiracle, passes through the cartilage of the brain case, and joins the internal carotid artery, having given off the ophthalmic artery (oph.a.) before passing through the cartilage. This artery gives a branch to supply the muscles of the lower jaw and proceeds forward to supply the rostral cartilages.