OSTEOLOGY AND SYNDESMOLOGY. 13 



the pivot. The best illustration of this articulation in the human subject is 

 that between the atlas and odontoid process of the axis or vertebra dentata. 

 Another example is seen in the superior radio-ulnar articulation. 



The ligaments which tie the bones together are of two kinds, capsular 

 and funicular. The former resemble a bag open at both ends, in which the 

 extremities of the bone forming the joint are included. The latter are 

 simple cords extending from one bone to another ; they may be either 

 cylindrical or flattened. They are variously placed ; in some instances 

 they are within the capsular ligament, in others on the outer surface, and 

 sometimes so blended with it as not to be separable without an artificial 

 dissection. The attachment of the head of the thigh bone to its socket in 

 the pelvis illustrates the capsular ligament, while that of the tibia to the 

 thigh furnishes an example of the funicular. Cartilages are also found 

 placed between joints for the purpose of diminishing friction. All the 

 movable articulations also have their surfaces covered with a layer of 

 cartilage of the most exquisite smoothness. In addition to this, there is 

 a closed sac called the synovial membrane, lining the articulation and 

 reflected over the inner faces of the capsular ligament and the articular 

 cartilages. This membrane, unlike the capsular ligament, has no opening- 

 whatever. Its whole inner surface appears to secrete the oily fluid called 

 synovia, whose object is to give suppleness and lubricity to the joint. 



The human skeleton, considered as a whole, may be conveniently divided 

 into head, trunk, and limbs, all together including from 213 to 217 distinct 

 bones. 



Projections on the bones either form articulations with other bones, and 

 are known as head, c#ndyle, &c., or they serve for the attachment of muscles 

 and tendons, in which case they become projections, processes, trochanters, 

 crests, lines, spines, ridges, &c. Depressions, cavities, or fissures are for the 

 attachment of muscles, the formation of articulations, or for the passage of 

 vessels and nerves. They are called furrows, impressions, holes, fissures, 

 canals, grooves, notches, &c. 



2. Bones of the Head. 



Beginning with the head we find a primary division into the bones of the 

 cranium or skull, and bones of the face. 



A. Bones of the Cranium. 



The cranium is composed of eight bones : the os frontis, the os occipitis, 

 the two ossa temporum, two ossa parietalia, the os sphenoides, and the os 

 ethmoides. The first of these, the as frontis, or frontal bone, is represented 

 in pi. 121, fgs. 1\ 4', 5*, and 7, from the anterior surface,/^. 8 from the 

 interior, and^^. 123, fg. 1, from below. It forms the whole anterior and a 

 portion of the superior lateral and inferior walls of the cranium, and may be 

 divided into the frontal, the two orbitar, and the nasal portions. Between 

 the two tables of the bone are to be found certain cavities or cells called 

 frontal sinuses {pi 12S, fig. 3'), lined by a mucous membrane. A median 



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