192 THE SKELETON. 



Structure. It consists of a nearly uniform dense cancellous tissue covered 

 by a thin compact lamina. The cancelli immediately beneath the anterior surface 

 are arranged parallel with it. In the rest of the bone they radiate from the 

 posterior articular surface toward the other parts of the bone. 



Development. By a single centre, which makes its appearance, according to 

 Be"clard, about the third year. In two instances I have seen this bone cartilagi- 

 nous throughout, at a much later period (six years). More rarely, the bone is 

 developed by two centres, placed side by side. Ossification is completed about the 

 age of puberty. 



Articulations. With the two condyles of the femur. 



Attachment of Muscles. To four : the Rectus, Crureus, Vastus internus, and 

 Vastus externus. These muscles, joined at their insertion, constitute the Quadriceps 

 extensor cruris. 



Surface Form. The external surface of the patella can be seen and felt in front of the 

 knee. In the extended position of the limb the internal border is a little more prominent than 

 the outer, and if the Quadriceps extensor is relaxed, the bone can be moved from side to side 

 and appears to be loosely fixed. If the joint is flexed, the patella recedes into the hollow 

 between the condyles of the femur and the upper end of the tibia, and becomes firmly fixed 

 against the femur. 



Surgical Anatomy. The main surgical interest about the patella is in connection with 

 fractures ; which are of common occurrence. They may be produced by muscular action ; that 

 is to say, by violent contraction of the Quadriceps extensor while the limb is in a position of 

 semi-flexion, so that the bone is snapped across the condyles ; or by direct violence, such as 

 falls on the knee. In the former class of cases the fracture is transverse ; in the latter it may 

 be oblique, longitudinal, stellate, or the bone variously comminuted. The principal interest in 

 these cases attaches to their treatment. Owing to the wide separation of the fragments, and 

 the difficulty there is in maintaining them in apposition, union takes place by fibrous tissue, 

 and this may subsequently stretch, producing wide separation of the fragments and permanent 

 lameness. Various plans, including opening the joint and suturing the fragments, have been 

 advocated for overcoming this difficulty. 



In the larger number of cases of fracture of the patella the knee-joint is involved, the car- 

 tilage which covers its posterior surface being also torn. In some cases of fracture from direct 

 violence, however, this need not necessarily happen, the lesion involving only the superficial 

 part of the bone; and, as Morris hns pointed out, it is an anatomical possibility, in complete 

 fracture, if the lesion involve only the lower and non-articular part of the bone, for it to take 

 place without injury to the synovial membrane. 



The Tibia (Figs. 133, 134). 



The Tibia (tibia, a flute or pipe) is situated at the front and inner side of the 

 leg, and, excepting the femur, is the longest and largest bone in the skeleton. It 

 is prismoid in form, expanded above, where it enters into the knee-joint, more 

 slightly enlarged below. In the male its direction is vertical and parallel with 

 the bone of the opposite side ; but in the female it has a slightly oblique direction 

 downward and outward, to compensate for the oblique direction of the femur- 

 inward. It presents for examination a shaft and two extremities. 



The Upper Extremity, or Head, is large, and expanded on each side into two 

 lateral eminences, the tuberosities. /Superiorly, the tuberosities present two smooth, 

 concave surfaces, which articulate with the condyles of the femur ; the internal, 

 articular surface is longer, deeper, and narrower than the external, oval from 

 before backward, to articulate with the internal condyle ; the external one 

 is broader and more circular, concave from side to side, but slightly convex from 

 before backward, especially at its posterior part, where it is prolonged on to the 

 posterior surface for a short distance, to articulate with the external condyle. 

 Between the two articular surfaces, and nearer the posterior than the anterior 

 aspect of the bone, is an eminence, the spinous process of the tibia, surmounted 

 by a prominent tubercle on each side, on to the lateral aspect of which the facets 

 just described are prolonged; in front and behind the spinous process is a rough 

 depression for the attachment of the anterior and posterior crucial ligaments 

 and the semilunar fibro-cartilages. The anterior surfaces of the tuberosities are 

 continuous with one another, forming a single large surface, which is somewhat 



