OSSEOUS SYSTEM. 201 



remain themselves partly cartilaginous. The number of the cranial 

 bones is small, and their homologies difficult to determine by com- 

 parison with those of other Osseous Fishes ; yet we find lateral 

 occipital elements, and a single bone forming the upper covering 

 of the skull } to this last there corresponds a similar bone at the 

 base of the cranium, which may be viewed as the body of the sphe- 

 noid. The bones of the face also attract our attention from their 

 peculiarities ; the superior maxilla appears to be wanting, while the 

 intermaxillary is present ; and there exists moreover a system of 

 labial cartilages, which, with the tooth-bearing lower jaw, exhibits 

 a relationship of structure with that of Chimaera. A more simple 

 quadratal cartilage unites the inferior maxilla to the skull. 



In the structure of the Vertebral Column of the Cartilaginous 

 Fishes we encounter peculiarities and differences in the several 

 orders and families, which are the more interesting when the de- 

 velopment of vertebrae comes to be studied, and the plan of their 

 formation followed out through the series of Vertebrate animals ; 

 an extensive subject belonging to the departments of philosophical 

 anatomy, and not to be entered upon here. 



In the Sturgeon and Chimaera the vertebral column is constituted 

 by a fibro-cartilaginous tube, which is filled with a gelatinous sub- 

 stance, and surrounded by a fibrous tunic, that is closed above to 

 form a tube for the spinal marrow. Upon the inferior surface of 

 this fibro-cartilaginous tube are situated the rudimentary basilar 

 parts of the vertebrae j they are united beneath by a membrane, 

 along which the aorta passes. Between the upper triangular pieces 

 of the arch other triangular pieces of cartilage (cart, inter crur ales) 

 are found, and the roof of the spinal canal is closed in by a series 

 of more elongated cartilages, above which there are placed in the 

 Sturgeon large spinous processes. The fibro-cartilaginous tube 

 of the Chimaera, very beautifully annulated by thin transverse 

 rings that were formerly falsely compared to vertebrae, remains in 

 a great measure exposed to view, and corresponds to that part in 

 the rest of the vertebrata, present only in their foetal condition, 

 but in Fishes more' or less persistent, namely the chorda dorsalis, 

 or central cylindrical axis, around which the formation of vertebrae 

 takes place. The persistent structure of the vertebral bodies in the 

 Sturgeon and Chimaera corresponds to that which exists only in 

 the foetal state of the Osseous Fishes. In these latter Fish, when 

 fully formed, the gelatinous tube is reduced to constricted masses of 

 gelatine, surrounded by the conical facets forming the bodies of the 



