132 COUES ON THE OSTEOLOGY 



impossible to present a complete myology, while such a procedure would be of doubtful 

 utility. The scope of the paper is perhaps expressed in its title. Whatever may be its 

 deficiencies or inaccuracies, it is offered in the hope that it may contribute its mite to the 

 sum total of our knowledge of the anatomy of the class. 



Of (he SMI 



In the adult skull, the various bones of the cranium are, with the exception of course 

 of the pterygoid and the tympanic elements of the temporal, so completely anchylosed that 

 even the traces of their original sutures are scarcely discernible. The same may be said 

 of the majority of the facial bones, especially the nasal, intermaxillary, and superior max- 

 illary. The fronto-maxillary " articulation," however, and the palato-pterygoid and tympano- 

 malar, remain freely movable. I will first notice the individual bones of the head, as well 

 those which are anchylosed as those which remain permanently separated, and afterwards 

 examine the skull, as a whole, upon its several aspects. 



The occipital forms the posterior, and a small part of the inferior, aspect of the skull. Its 

 basilar process is nearly smooth and fiat, somewhat of a diamond shape, bounded anteriorly 

 by the occipito-sphenoidal anchylosis, more laterally by the petrous portion of the temporal, 

 posteriorly by the atloid condyle and foramen magnum. Just anterior to the condyle 

 there are two considerable depressions for ligamentous attachments; and just externally to 

 these, two slight elevations. Laterally, the occipital spreads out and rises into two promi- 

 nent processes, the apices of which are rough for the attachment of muscles. From these con- 

 dyles and from the basilar process, the " spinous " element of the bone arches upwards toward 

 the parietal, leaving inferiorly the large orifice, — the foramen magnum. On either side 

 these " spinous " plates are much depressed and rough for the attachment of muscles, 

 and are separated from the parietal bones by elevated curved crests. On the median 

 line they rise up to form an arched longitudinal elevation. The foramen magnum is broadly 

 oval iu shape, its long axis being antero-posterior. Above, its margins are very thin, being 

 formed by the thin " spinous " plates of the occipital ; they become laterally considerably 

 thicker. Inferiorly, the edge of the foramen is occupied by the single condyle forming the 

 occipito-atloid articulation. Its face is exceedingly convex ; its general outline a semilune, 

 the cornua presenting upwards, the greatest convexity directly downwards. Around the 

 foramen magnum are several other foramina, for the transmission of some of the cranial 



nerves. 



Sphenoid. The basilar process of this bone projects directly forwards from the basilar pro- 

 cess of the occipital, in the median line, having on either side the pterygoid and palate 

 bones, from both of which it is entirely separated. In this species, in which the orbits are so 

 defective as to their bony parietes, it forms nothing of the floor of the orbits, but, by a vertical 

 lamella of bone which projects forward, it contributes to form the inferior portion of the 

 very deficient septum which exists between the orbits. From the posterior part of the base 

 of the bone, the two " orbital " processes or plates extend upwards, forwards, and outwards, 

 as thin lamellae. They form the posterior walls of the orbits, separating them from the 

 cranial cavity. Each is pierced near the median line, at its lower border, by the very large 

 subcircular optic foramen ; and external to these, by a smaller opening for the ophthalmic 

 division of the fifth nerve. The second and third divisions of the fifth together perforate 

 the bone much further back and more externally, in the depression just above the body 



