OSSEOUS SYSTEM. 199 



an orbitar process. United to the anterior extremity of the cranium 

 we meet with a deep hollow leaflet of cartilage, forming the nosal 

 fossa. The upper jaw is constituted by a narrow arch of cartilage, 

 occasionally, however, deep, as in the Sharks, and of a semiluuar 

 form; it is beset completely, both upon its edge arid posterior wall, 

 with teeth. A quadratal cartilage, more simple and elongated, is 

 lodged in a posterior lateral depression in the skull, and articulates 

 with the lower jaw, an arch provided with teeth, and composed of 

 two lateral halves like the upper. There occur, moreover, in the 

 Rays small palatal cartilages, as also peculiar cartilages belonging 

 to the spiracles, and which correspond somewhat to the pterygoid 

 bones or processes in the Osseous Fishes. The intermaxillary bone 

 must be regarded as absent, if we do not consider it united with the 

 superior maxilla in the arch of cartilage just described. In the 

 Chimaerae the skull is very peculiarly formed, being provided with 

 distinct convoluted nasal cartilages, while upon the fore part of the 

 head stands a style-shaped piece of cartilage. 



Furthermore, there exists in many of the Sharks and Chimceras 

 a peculiar system of labial cartilages, which is wanting in the Rays 

 and Sturgeons ; the question of its homology has given rise to 

 various incorrect, speculations ; a portion of it was regarded formerly 

 by some anatomists as belonging to the maxillary apparatus. It 

 consists of several more or less elongated muzzles of cartilage vary- 

 ing in form and particularly remarkable in the Chimaera, which rest 

 externally and laterally against the upper and lower jaw. In Acan- 

 thias and other genera, for example, a lower labial cartilage is to be 

 distinguished lying upon the inferior, and a superior upon the upper 

 maxilla, and occasionally, as in Scymnus, Chimaera, a third carti- 

 lage situated above the latter one. Among the Rays, it is only in 

 Narcina that small labial cartilages are met with. In them and in 

 the true Electric Rays (Torpedo) there is situated in front of the body 

 a cartilaginous production of the muzzle which unites the pectoral fins 

 to the skull. 



Still more abnormal is the structure of the cranium in the Cyclo- 

 stomi, and in them we are again met by numerous varieties in the 

 structure of the buccal cartilages. With this group, indeed, all at- 

 tempts to draw any analogy or comparison with the typical Fishes 

 must be laid aside. 



The craninm of Petromyzon marinus and fluviatilis consists of a 

 hard, nearly osseous brain-capsule, having a detached flattened basi- 

 lar portion, that gives off in the direction backward a pair of pro- 



