[ 166 J 



XXI.— THE OSTEOLOGY AND AETHHOLOGT OF THE HAD- 

 DOCK {GADUS JEGLEFINUS). Br H. ST. JOHN 

 BROOKS, B. A., M. B., B. Ch., Seniok Modeeatok in 

 Natural Science, Univ. Dub. ; Demonstrator oe ANAioMr, 

 Carmichael College oe Medicine. (Plates Y.-IX.) [Com- 

 municated by Alexander Macalister, M. D., E. B,. S.] 



[Head, November 19, 1883.] 



In this Paper is given a detailed description of the osteology and 

 arthrology of a single type of Teleostean fish. In a work of this 

 kind there is not likely to be found anything new, although 

 several things in it are new to me, such as the existence of a 

 cartilaginous rod passing from the atlas into the exoccipital bone, 

 the peculiarity of the articulation of the first rib, the existence of a 

 structure which is probably the homologue of the lower labial 

 cartilage of the Elasmobranch fish, &c. 



It will be convenient to adopt the usual classification of the 

 vertebrate skeleton into axial and appendicular parts — the former 

 comprising the skull and vertebral column ; the latter, the shoulder 

 and pelvic girdles, with the bony axes of the limbs-: to these may. 

 be added, in fishes, the interspinous bones and fin-rays. 



The skull may be divided into the cranium, or brain- case, and 

 the bones of the face, the latter including the suspensorium and 

 gill arches and the operculum,. or gill cover. 



The cranium is composed of the following bones : the supra- 

 occipital, frontal, and mesethmoid form the roof from behind for- 

 wards in the middle line ; more laterally, the parietal, epiotic, 

 pterotic, and sphenotic, the two latter appearing also in the lateral 

 walls, and the epiotic in the posterior wall ; laterally the skull is 

 bounded by the pterotic, opilthotio, sphenotic, prootic, alisphenoid, 

 and prefrontal or ectethmoid ; posteriorly by the supraoccipital, 

 epiotic, exoccipital, and small parts of opisthotic and basioccipital 

 (see PL v., figs. 1, 2, and 3). The floor is formed by the basi- 

 occipital, prootic, and prefrontal, and is closed below the middle 

 portion by a membranous interorbital septum. 



