VERTEBRM 27 



mentary laminfe and processes. There is no necessity for noticinir the sacrum, 

 the five pieces of which form one bone— a feature that markedly distinguishes 

 it from the other regions of the vertebral column. But these few distinctive 

 characteristics do not satisfy the requirements of descriptive anatomy ; so that 

 it is necessary to undertake a more extensive study of each of these regions. 



1. Cervical Vertebra. 



General Characters. — These vertebrae, the longest and thickest in the 

 spine, present generally a cubical form. They are usually distinguished from the 

 vertebrae of the other regions by the following characters : The inferior spine of 

 the body is strongly marked, especially behind, where it terminates in a small 

 tubercle. The head is well detached from the remainder of the bone, and 

 describes a very short curve. The posterior cavity, 

 wide and deep, represents a veritable cotyloid de- ^'g- ^^• 



pression, which is too large to fit the head exactly; 

 the intermediate fibro-cartilage on these two sur- j 

 faces is also of a great thickness. The spinous 

 process forms a simple roughened, and but slightly 

 prominent, ridge. The transverse processes, very 

 developed, are elongated in an antero-posterior 

 direction, and inclined downwards. In this region 



they are designated the trachelian processes, be- ^ cervical vertebra. 



cause of their relations with the trachea : a , « • o 



' 1, bupenor spinous process; 2, an- 



foramen that traverses them from before to terior articular processes ; 3, pos- 

 behind at their base has been, for the same ^^'■'°'" a'ti'^''-^'; I'l-cesses ; 5, an- 



, , , - tenor convex face of boily; b, 7, 



reason, named the tracfielian joramen {vertehral transverse processes, with their 



forctmen). The articular processes, large and tubercles or rudimentary ribs; 8, 



prominent, are inclined downwards and inwards. p"?terTor face. °' ''''"' ' ^' '""'''' 

 The notches are wide and deep. 



Specific Characters. — The seven cervical vertebrse are reckoned from 

 before to behind, and receive numerical names indicating their place in the 

 region. 



First. — The first vertebra of the neck, which has been named the atJas,^ 

 deserves a very careful description. At first sight there is recognized the great 

 development of its transversal diameter, the considerable dimensions of the 

 spinal foramen, and the thinness of its body. The intra-spinal face of the latter 

 is divided into two portions by a transverse ridge : one anterior, furnished with 

 hgamentous imprints, exhibits, laterally, two deep excavations, which lodge the 

 venous sinuses ; the other, posterior, is smooth and concave from side to side, 

 and forms an articular surface into which is received the odontoid process of the 

 axis ; this surface takes the place of the cotyloid cavity. The inferior spine of 

 the body appears as a large tubercle (Fig. 15, 6). The head is absent, and is 

 replaced by two concave facets. The anterior articular processes have their 

 ghding surfaces looking downwards ; they are joined to the two preceding facets 

 to constitute two large diarthrodial cavities, which articulate with the occipital 

 condyles (Fig. 15, 1). There is no spinous process, but a roughened surface 

 instead. The transverse processes are large, flattened above and below, inclining 

 forwards and downwards, and are provided with a thick ruT'ied lip. Posteriorly, 



' Rudimentary ribs are sometimes attached by ligaments to the ends of the transverse 

 processes (.LesbreX 



