| OCR Text |
Show 6 DR. J. P. G E M M I L L O N [May 12, bulars (PI. I. fig. 1). The fifth nerves emerge through deep grooves between the trabecular and the auditory capsules, while the vagus and glosso-pharyngeal nerves pass out together through a foramen in the cartilage connecting the auditory capsules with the parachordals. A single opening in the floor of the capsules on either side gives passage to the internal jugular vein and the facial nerve. The nasal cartilage is connected with three pairs of bars: (1) the trabecular cranii, (2) the palatoquadrates, and (3) the supraorbitals. These last pass backwards along the dorsolateral angles of the brain to join the anterior part of the auditory capsules on either side. Over the pineal body and the third ventricle the supraorbitals are connected together by a bridge of cartilage, but no such legmen exists over the cerebral or optic lobes, the spaces left uncovered being the anterior and the middle fontanelles (PI. I. fig. 2, fl,f2). The hyomanclibulars are connected with (1) the outer aspect of the auditory capsules, (2) the posterior ends of the palatoquadrates, and (3) the inter-hyals. The Meckelian bars are slender, and meet below the mouth in a symphysis. Posteriorly they articulate with the palatoquadrates, but not with the hyomandibular or interhyal cartilages. In the hyoid arches, glossohyals, hypohyals, cerato-hyals, and interhyals can be distinguished. The branchial cartilages are five in number, and have the usual forms and relations. The pectoral girdle is represented by a comparatively short bar of cartilage on either side-the coraco-scapular-and is far from being a complete arch ventrally. The limb-cartilage is an unsegmented plate continuous with the coraco-scapular bar. The notochord consists of pith-like tissue surrounded by a very firm capsule, and its anterior end is embedded in the fused parachordal cartilages. In the position of each future vertebra there are four cartilaginous nodules, placed respectively at the dorsolateral and ventro-lateral corners of the notochord, and prolonged into processes for the neural and haemal arches (PI. I. fig. 7). The anatomy of the central nervous system and of the organs of special sense, and of the heart and blood-vessels, is, with certain differences in the relative size of parts, practically the same as in the adult condition. As regards the aortic roots, it may be stated that the first root, i. e. the first branchial vein, gives off the hyoid and carotid arteries and then passes backwards to join the second root. The resulting trunk bends inwards to the middle line, and, meeting with its fellow from the opposite side, forms the upper part of the aorta. This part is next joined on either side by a trunk formed by union of the third and fourth roots. The carotids pass forward beneath the parachordals and, traversing the pituitary space from below, reach the base of the brain. The hyoicl artery arises from the first aortic root at its ventral end, perforates the hypohyal, runs up along the hyoid bar, and, after passing through a foramen in the hyomandibular, is continued mainly into the pseudobranch. The efferent vessel of the pseudo-branch passes forwards and inwards, traverses the pituitary space |
