ABTICULATIONS OF THE HEAD. ]35 



another, and the superspinous ligament, becoming very tense, soon imposes 

 limits to this movement. 



Extension is effected by an inverse mechanism, and is checked by the 

 tension of the common inferior ligament and the meeting of the spinous 

 processes. 



Lateral inclination takes place when the spine bends to one side. This 

 movement is very easily executed in the cervical and coccygeal regions, but 

 is arrested by the ribs and the costiform processes in the dorso-lumbar 

 region. 



A circumflex movement is possible at the two extremities of the vertebral 

 column—neck and tail; for they pass easily from extension to lateral 

 inclination, and from this to flexion, etc. 



Owing to the elasticity of the intervertebral fibro-cartilages, the spine 

 is endowed with a very limited amount of rotation, or rather of torsion. 



For the special study of the movements of each spinal region, reference 

 must be made to what has been already said (page 29) regarding the 

 mobility of this column. 



In the Ox the intervertebral discs are much thicier than in the Horse. The common 

 inferior vertebral ligament is very strong in the lumbar region. The superspinous 

 dorso-lumbar ligament is composed of yellow elastic tissue. Tlie cervical ligament 

 is much more developed than ia Solipeds, in consequence of the greater weight of 

 the head ; and it presents a conformation altogether special, which M. Leooq has made 

 known in the following terms : " On leaving the withers, the superspinous ligament 

 ceases to cover the head of the spinous processes, and extends from each side in a wide 

 and strong band, taking points of attachment on the sides of the processes, and becoming 

 separated, on leaving that of the first dorsal vertebra, into two parts — a superior and 

 inferior. The first reaches the cervical tuberosity in the form of a thick cord united to 

 the cord of the opposite ; the other thins off into a band which is attached to the posterior 

 half of the spinous process of the axis and to that of the third and fourth vertebrse. A 

 production of the same natvu'e, an auxiliary to the principal portion, leaves the anterior 

 border of the spinous process of the first dorsal vertebra, and is attached to that of the 

 fourth, fifth, sixth, and seventh vertebrae. The superior border of this auxiliary liga- 

 mentous production is concealed between the two lamina of the principal ligament." ' 



The Pig, remarkable for the shortness of its neck and the limited movements of this 

 region, does not show any cervical ligament, properly so called. It is replaced by a 

 superficial fibrous raphe extending from the occipital bone to the spinous process of the 

 first dorsal vertebra. 



The Cat has no cervical ligament, and shows, instead, a raphe' like the Pig. In 

 the Dog the ligament is reduced to a simple cord, continued from the dorso-lumbar 

 ligament, and which goes no further than behind the spinous process of the axis In 

 the Cat the interspinous ligaments are replaced by small muscular fasciculi ; with the 

 Boa this substitution only takes place in the cervical region. The laminie ot tbe Urst 

 coccygeal vertebrae possess the principal characters which distinguish perfect vertebrsB 

 and are united by vestiges of the articular bands which exist m the other regions of 

 the spine. 



Aeticlb II.— Abtioulations op the Head. 

 We will first study the two extrinsic articulations which, are the centre 

 of the movements of the head on the spine— the atlo-axoid and occipito-atloid 

 articulations. Afterwards, we will pass to the examination of the joints which 

 unite the different bones of the head. 



1. Atlo-axoid Articulation. 



f V nnrniion It suffices to remove the soft parts from around the articulation to 



the interannular, the interspinous, and the inferior odontoid ligament. To examine 



'Journal de Me'decine Ve'te'rinaire ' (Lyons, 1848), p. 122. 



