18 CLASS XIV. 



fingers alone of the posterior extremities are present, which cor- 

 respond to the rays of the ventral fins. 



The comparison of the skull-bones of fishes with those of the skull 

 of the other vertebral animals, is a rock upon which the ingenuity 

 of many naturalists has been wrecked. The skull of bony fishes con- 

 sists of a much greater number of bones than that of man; and this 

 peculiarity may in part be explained on the supposition that what in 

 the embryo state of man and mammals are distinct points of ossi- 

 fication, in fishes persist as distinct bones during their entire life. 

 Chiefly numerous are the bones which collectively represent the 

 temporal bone in man 1 . On a superficial inspection the difficulty 

 appears to be rendered still greater by the bones related to the 

 largely developed tongue-bone and to the respiratory apparatus, 

 which are connected with the bones of the skull. Moreover, some 

 bones, which do not correspond to any in the skull of higher ver- 

 tebrate animals, are to be referred to the dermal skeleton 2 . 



At the base of the skull three bones are readily distinguished, 

 placed in front of one another in a row; the basal piece of the 

 occipital bone, the body of the sphenoid, an elongated bony lamina 

 channelled above, and the vomer, which becomes broader and thicker 

 forwards, and often on its under surface is armed with teeth. The 

 basal piece of the occipital bone is a true body of a vertebra, and 

 has behind a conical cavity for connexion with the first dorsal 

 vertebra. Above it on each side lies a lateral occipital bone or 

 articular portion (occipitale laterale, superior vertebral arch), which 

 corresponds with the condylo'id portion of the human occipital bone. 

 These bones approach one another above, but leave between them 

 and the basal piece below an aperture nearly triangular (foramen 

 magnum], through which the spinal marrow passes into the cavity of 

 the cranium; they are perforated by a conspicuous aperture, through 

 which the nervus vagus, and a smaller one through which the 

 n. glossopharyngeus, leaves the skull. Above the occipital foramen 

 is an unpaired bone, which sometimes forms a sharp crest in the 



1 On this bone, and on the skull of vertebrate animals in general, much that is 

 interesting is to be found in the celebrated work of E. HALLMANN Die vergleichende 

 Osteologie des Schldfenbeins, mit 4 Kupfertafeln. Hannover, 1837, 4to. 



2 Without greater prolixity than this handbook permits we cannot offer more precise 

 explanations of the names by which we describe the bones of the skull, and therefore 

 must refrain also, for the most part, from criticising other designations of them. 



