212 DESCRIPTION OF A SPECBIEN 



the median line is 4 3-4 inches. In a straight line between the ends the bone is 24 1-2 

 inches broad ; following the convexity 31 inches. The circumference of the thyro-hyal at 

 its extremity is 7 inches, and midway between this point and the centre of the bone 

 11 1-4 inches. 



The Stylo ILjal. — This is 15 inches long in a straight line, and 16 inches following the 

 convexity. It is compressed above and below, except at the very inner end where the 

 vertical diameter is the greatest. The outer end is but 1 inch thick. 



D 



Vertebra. 



The vertebral formula is 7 cervical, 15 dorsal, 15 lumbar, 26 caudal. As the cervical 

 vertebrae are always described as of particular importance for classification in spite of the 

 considerable variations which they exhibit, it is advisable to describe each one separately, 

 so that accurate comparisons can be drawn between corresponding bones in different skel- 

 etons. The vertebrae of the other regions will be considered in a different manner. 



Atlas. — This bone, like that of the Rosherville specimen described by Mr. Murie (P. Z. 

 S., 1865, p. 217), resembles Gray's figure of the atlas of the P. Dugnidii rather more 

 closely than that of the P. antiquorum in the thickness and obtuseness of the transverse 

 processes, the greater length of the neural spine and the greater interval between the in- 

 ferior ends of the anterior ai'ticular surfaces. The anterior aspect is formed by the articu- 

 lar surfiices and the transverse processes. The greatest length of the articular surfices is 

 10 1-4 inches, the greatest breadth 5 1-4 inches ; they are deeply concave and surrounded 

 by a slight groove, separating them from the outer aspects of the bone. The superior ex- 

 tremities of these cavities are 5 inches apart ; the inferior 3-4 inch. The opening 

 between them is 7 1-4 inches long ; it becomes constricted about the middle, the superior 

 half forming the continuation of the spinal canal, the inferior being closed by the body of 

 the axis. 



The posterior surface presents the same general outline, but the two articular surfaces 

 are united into one by an isthmus 1 1-2 inches in breadth, across the inferior part of the bone. 

 They do not form the lateral boundaries of the canal, but are separated from it by about 1 

 inch of smooth bone. The arch is marked above by a longitudinal spine in the median line 

 with a prominence at either end. The anterior border is sharp, but presents a tubercle at 

 the point of union with the articular surfaces, which forms the roof of a canal opening 

 directly external to it (PL vi, fig. 4 a). The lower edge of the arch is thick and presents a 

 smooth surfice (PI. \i, fig. 4 h) on each side of the median line for articulation with corres- 

 ponding ones on the arch of the axis in serial homology with the z^-gapophyses. There is a 

 slight prominence projecting backward in the median line. The tranverse process has a 

 broad vertical base from which it gradually tapers. Towards its point it is twisted upon 

 itself so that the anterior surface of the base becomes the inferior near the apex, and the 

 posterior in like manner becomes the superior. On the superior aspect of the bone the 

 tranverse process springs from a prominent tubercle (PL vi, fig. 3 a, fig. 4 c) on the posterior 

 border. Nutrient foramina enter the bone on the front and back of the base of the trans- 

 verse process. 



Axis. — The Boston whale, unlike the Rosherville one, resembles in this point the draw- 

 ing of the P. Duguidii and not that of the P. antiquorum ; Gray's drawing of the former 



