THE ARTICULATIONS OF THE HORSE— INTERCENTHAL ARTICULATIONS 



211 



THE ARTICULATIONS OF THE HORSE 

 Joints and Ligaments of the Vertebra 



The movable vertebrae form two sets of articulations, viz., those formed by the 

 bodies, and those formed by the articular processes of adjacent vertebra the 

 former are termed intercentral, and the latter intemeural. Associated with these 

 are ligaments umtmg the arches and processes; some of these are special, i. e con- 

 faned to a single joint, while others are common, i. e., extend along the entire ver- 

 tebral column or a considerable part of it. The joints between the atlas and axis 

 and between the former and the skull require separate consideration. 



Supraspi- 

 nous liga- 

 ment 



INTERCENTRAL ARTICULATIONS 



These are amphiarthroses, formed by the junction of the extremities of the 

 bodies of adjacent vertebrae. The articular surfaces in the cervical region consist 

 of a cavity on the posterior 

 end of the body of the anter- 

 ior vertebra, and a correspond- 

 ing convexity or head of the 

 succeeding vertebra. In the 

 other regions the surfaces are 

 much flattened. The uniting 

 media are : 



1. The intervertebral 

 fibro-cartilages (Fibrocartila- 

 gines intervertebrales). Each 

 of these is a disc which fits into 

 the space between the bodies 

 of two adjacent vertebrae, to 

 which it is intimately attached. 

 The discs are thinnest in the 

 middle of the thoracic region, 

 thicker in the cervical and lum- 

 bar regions, and thickest in the 

 coccygeal region. " Each consists of a peripheral fibrous ring 



Fig. 230. — Sagittal Section of Last Two Thohacic and First 

 Lumbar Vertbbr.e, showing Ligaments and Spinal Cord 

 (Medulla). (After Schmaltz, Atlas d. Anat. d. Pferdea.) 



(Annulus fibrosus) 



and a soft central pulpy nucleus (Nucleus pulposus). 



The fibrous ring consists of laminae of fibrous tissue and fibro-oartilage, which pass obKquely 

 between the two vertebrae and alternate in direction, forming an X-shaped arrangement. The 

 central part of the ring is largely cartilaginous, and gradually assumes the character of the pulpy 

 center. The latter is very elastic and is compressed, so that it bulges considerably from the sur- 

 face of sections; it consists of white and elastic fibers, connective-tissue cells, and pecuHar clear, 

 transparent cells of various sizes. It is a remnant of the notochord. There are joint cavities in 

 ' the cervical intercentral joints, and in those between the last cervical and the first thoracic, and 

 between the last lumbar and the sacrum. 



2. The ventral longitudinal ligament (Lig. longitudinale ventrale)i lies on the 

 ventral surface of the bodies of the vertebrae and the intervertebral fibro-car- 

 tilages, to which it is firmly attached. It begins to be distinct a little behind the 

 middle of the thoracic region, and is at first a narrow, thin band. Further back 

 it becomes gradually thicker and wider, and terminates on the pelvic surface of 

 the sacrum by spreading out and blending with the periosteum. It is strongest in 

 the lumbar region, where the tendons of the crura of the diaphragm fuse with it. 



3. The dorsal longitudinal ligament (Lig. longitudinale dorsale)^ lies on the 

 floor of the vertebral canal from the axis to the sacrum. It is narrow over the mid- 



' Also termed the inferior common hgament. 

 2 Also termed the superior common ligament. 



