34 



THE SKELETON OF THE HORSE 



the dorsal. On its lower surface is the ventral tubercle (Tuberculum ventrale). 

 into which the terminal tendon of the longus colli muscle is inserted. The upper 

 face has posteriorly a transversely concave articular surface (Fovea dentis), on 

 which the dens or odontoid process of the axis rests. In front of this is a transverse 

 rough excavation for the attachment of the odontoid ligament. 



The wings (Alse) are modified transverse processes. They are extensive curved 

 plates which project outward, downward, and backward from the lateral masses. 

 The dorsal surface is concave. Between the ventral aspect of the wing and the 

 lateral mass is a cavity, the fossa atlantis ; in this there is a foramen which opens 

 into the vertebral canal. The border is thick and rough. Two foramina perforate 

 each wing. The anterior one, the foramen alare, is connected with the interverte- 

 bral foramen by a short groove. The posterior one is the foramen transversarium. 



Development. — The atlas ossifies from three or four centers, one or two for 

 the ventral arch, and one on either side for each lateral mass, wing, and half of the 

 dorsal arch. At birth the bone consists of three pieces — the ventral arch and two 

 lateral parts, which are separated by a layer of cartilage in the dorsal median line. 

 These parts are usually fused at about six months. 



Axis 



Atlas 



?qrr^ 



I ntervertebral for. 

 Post, artic. process 

 ! A7it. artic. process 

 Dorsal crest 



Post, artic. 

 process 



1 7iter vertebral ' 



foramen Furanun 



transversarium 



I ntrr vertebral 

 foramen Foramen 



transversarium 

 Ventral crest 



Fig. 11. 



-First Three Cervical Vertebra of Horse, Lateral View. 



Pferdes.) 



Ventral en s! ■"""'^^ * 



(After Schmaltz, Atlas d. Anat. d. 



The Axis 



The axis (Epistropheus) is the longest of the vertebrae, and is characterized 

 by the presence of the odontoid process, which projects from the anterior part of 

 the body. 



The body has a median ventral crest which terminates in a tubercle behind. 

 The anterior extremity presents centrally the odontoid process (Dens) ; this has a 

 convex articular surface ventrally for articulation with the ventral arch of the atlas, 

 and two rough depressions for the attachment of the odontoid ligament dorsally. 

 Flanking this on either side are the modified anterior articular processes, which 

 have saddle-shaped articular surfaces confluent below with that of the dens. The 

 posterior extremity has the usual cavity. 



The arch presents in the young subject a notch on each side of its anterior 

 border; this is converted into a foramen by a ligament which usually ossifies later. 

 The posterior border has the usual notches. 



The posterior articular processes are typical. 



Tlie transverse processes are small, single, and project backward. The 

 foramen transversarium is small. 



The spinous process is very large and strong. Its free border is rough, thickens 

 posteriorly, and is continued to the articular processes by two ridges. The lateral 

 surfaces are concave and rough for muscular attachment. 



