SCIirLTK, SKI WHALK. -is? 



face for the axis is narrower than in the adult. Its long axis is dorso- ventral. It sends upon 

 the ventral arch a slender prolongation, which fails by a narrow interval of meeting its fellow of 

 the opposite side. 



The capsule of the atlanto-occipital articulation is very strong and is attached round the 

 margin of the articular surface, a faint groove being present on the lateral mass for its reception. 

 The space between the lateral masses entally is filled with strong connective tissue, of which the 

 bundles are for the greater part oriented transversely and seem therefore to represent the trans- 

 verse ligament of the atlas. This is broad and thin and passes us Struthers has shown rostral 

 and not dorsal to the odontoid process. Its margins are concave; between the ventral one and 

 the arch of the atlas, the ligamentum apicis dentis passes to its insertion on the basioccipital 

 in the fossa between the condyles and the ventral to the foramen magnum. In cross section 

 this ligament appears to contain a cavity, which is probably related to the degeneration of the 

 notochord, about which the ligament develops. 



Dimensions of (he atlas. 



mm. 



Hreadtli between tips of transverse processes 21 



I torso-ventral diameter 18 



I )orso- ventral diameter of neural canal 12 



Dorso-ventral diameter of its dorsal compartment 6 



Dorso-ventral diameter of its ventral compartment 



Transverse diameter of its dorsal compartment - 7 



Transverse diameter of its ventral compartment 



Length of articular surface for occipital 13 



Greatest breadth of articular surface for occipital 5 



Axis: - - This vertebra is characterized by the large size of its transverse processes, which 

 in consequence of a smaller foramen are more massive than those of the succeeding vertebrae. 

 They are directed obliquely caudad and laterad in the form of plates with rostral and caudal 

 surfaces. Their extremities are broad and rounded and contrast in this respect with the more 

 pointed form of the adult. The spinous process is feebly developed. The articular surfaces 

 for the atlas are concave from side to side, dorso-ventrally they appear flat. Their ventral 

 extremities are not confluent but are separated by a very narrow interval. They differ from 

 those of the adult chiefly in the regularity of the curve of their lateral contour. The space 

 between them rises very slightly in a low cone, the odontoid process. Dorso-ventrally the axis 

 measures 16.5 mm., transversely 27 mm. The spinal canal in the corresponding diameters is 

 6 mm. by 7 mm. 



Ribs: There are thirteen pairs of thoracic ribs, and in addition a well developed cervical 

 rib fused with the first of the thoracic series. The thoracic ribs with the exception of the first 

 are a series of slender bars increasing in length to the seventh and then diminishing. The last, 

 however, is not greatly reduced. The last three ribs diverge by reason of the increasing obli- 

 quity of the more caudal ones,, so that the corresponding intercostal spaces broaden ventrad; 

 the last rib makes an angle of something under 45 with the horizontal. The second and third 

 ribs have well developed necks and heads, the latter articulating with the vertebral centra; 

 that of the second articulates with the second thoracic vertebra near its rostral margin impinging 

 slightly upon the preceding intervertebral disk. The head of the third rib articulates with the 

 disk between the third and fourth vertebrae, touching their bodies to only the slightest degree. 



