188 PISCES. 



tilage, and opposed to the pharyngeal teeth. The two latero-inferior 

 occipital elements rest upon this basilar portion of the bone, and, 

 analogous in part to the articular or condyloid pieces of the higher 

 Vertebrata, concur in forming the lateral and superior parts of the 

 occipital bone, and leave between them the foramen magnum for the 

 exit of the spinal cord. Each of these pieces is perforated in the 

 Carp by a large oval opening, situated laterally above the foramen 

 magnum, and which remind us of similar apertures in many Wading 

 and Aquatic Birds. Superiorly to the above pieces are placed the 

 two latero-superior elements, which in many cases receive the mem- 

 branous semicircular canals of the auditory organ, and therefore 

 represent, in some respects, certain portions of the temporal; they 

 have been viewed, accordingly, by some anatomists as mastoid 

 bones. These two pieces are generally smaller than the inferior 

 pair, and correspond in part to the squamous element of the occi- 

 pital, which is here, however, principally formed of a single plate of 

 bone. This, the supra-occipital, is usually provided with a strong 

 crest or spine-shaped process for the attachment of the nuchal 

 muscles. This crest is more strongly developed in the Bream than 

 in the Carp, and to a still greater degree in Coryphaena, Chretodon, 

 &c. It corresponds to the spinous processes of a vertebra. 



The Sphenoid is divisible into seven pieces, three of which are in 

 pairs. The single body of the sphenoid is mostly of a very elon- 

 gated form, frequently also of great depth, laterally compressed 

 and keel-shaped, e. g. in Anarrhicas. It forms the largest and 

 chiefly the middle part of the base of the skull, abuts posteriorly 

 against the body of the occipital, and in front against the vomer. 

 It supports in the direction upward the two ala majores, if we do 

 not regard these as partly united to the temporal bone. At the 

 point posteriorly where these pieces come in contact with the pe- 

 trous bone, they have a notch through which the second and third 

 branch of the trigeminal nerve issue from the skull. Still further 

 upward and forward are situated the ala minor es, which are fre- 

 quently two in number, but often replaced, as in the Carp, by a 

 single osseous leaflet, excavated superiorly by a keel-shaped groove ; 

 in other Fish they coalesce at an early period of existence into one 

 bone. All the above-named parts of the sphenoid are, like those of 

 the occipital, united together, and with the rest of the cranial bones, 

 by suture. This is not, however, the case with the two pairs of 

 inferior wings or pterygoid processes, which, of considerable size, 

 abut against the middle part of the inferior surface of the body of 



