Macalister — Oil the Morphology of Joints. 783 



cular septa. Where these partitions dip in and come in contact with 

 the capsules of joints they adhere thereto, and form, a series of acces- 

 sory Ligaments ; thus the pubo-femoral accessory ligament of the hip 

 is formed by the pectineal portion of the fascia lata, and the sciatic 

 ligaments are genetically connected with the inferior involution of the 

 glutaeal fascia. 



4thly. Those derived from degenerated muscles. Of these, in man 

 we have representatives in the intercostal expansion in front of the 

 external intercostal muscle, and in the posterior sacro-coccygeal liga- 

 ment ; but in lower animals, as in the horse's foot, we find a striking 

 example. 



The articular cavities are primarily limited to the spaces between 

 the ends of the bones ; but, secondarily, from the formation of bursas, 

 and from the communication of these with the joints, the cavity 

 becomes extended. The shoulder and the subscapular bursa is an 

 opposite illustration. 



A special case of such enlargement occurs in the knee-joint, which 

 is peculiar in its development, as I shall have opportunity of showing on 

 a future occasion when describing my sections. The femoral condyles 

 approach the tibia, each independently, and two independent cavities are 

 formed, between which a ridge of the primitive embryonic disk becomes 

 transformed into fibrillar tissue, forming the crucial ligaments ; while 

 the margins of the original inter-articular discs persist as the menisci. 

 The capsule originally flows around the joint close to these, and the 

 tendons all lie external thereto. In the quadriceps tendon a sesamoid 

 cartilage develops (the patella), between which and the front of the 

 capsule there forms a large bursal cavity, under which the front wall 

 of the proper capsule becomes deficient, its shreds persisting as the 

 mucous ligament, and the alar ligaments, and the Haversian pellet of 

 fat. In many animals the tendon of the extensor digitorum arising 

 from the femur passes down in front of the joint under the quadriceps. 

 In the frog this is in front of the anterior wall of the capsule ; but in 

 lizards the wall is deficient behind it, and so it passes free through 

 the joint, as it does in so many other animals. 



In the second part of this Paper I purpose entering into detailed 

 descriptions of the histories of the individual articulations. 



W. I. A. I'KOC. SEU. II., VOL. III. — SCIEXCE. 



4G 



