644 EMBRYOLOGY. 



1. The diaphysis of the humerus ossifies in the eighth week. Epiphysial 

 nuclei are not formed until after birth, at the end of the first or beginning of 

 the second year. In the second year there appear accessory nuclei in the 

 tuberculum majns and minus ; during and after the fifth year in the epicondyles 

 also. 



2. The diaphyses of the radius and ulna also begin to ossify in the eighth 

 week. Epiphysial nuclei do not appear until between the second and the fifth 

 years. Accessory nuclei are observed rather late in the styloid processes. 



3. The metacarpals begin to ossify in the ninth week, but, with the 

 exception of the metacarpal of the thumb, there arises only one epiphysis, 

 which is at the distal end. This acquires in the third year its own centre of 

 ossification. 



4. The ossification begins in the phalanges at the same time as in the 

 metacarpals. 



5. The femur begins to ossify in the seventh week. A short time before 

 birth there is formed in the distal epiphysis a centre of ossification, which is a 

 part of the evidence that a child has been carried to the full time, and therefore? 

 possesses a certain importance for forensic purposes. After birth an epiphysial 

 nucleus soon appears in the head of the fermir. Accessory nuclei are formed 

 in the fifth year in the trochanter major, in the thirteenth or fourteenth in 

 the trochanter minor. 



6. Tibia and fibula acquire epiphysial nuclei in the first and third years after 

 birth, first at the proximal, then at the distal end, the ossification in the 

 fibula occurring about a year later than that in the tibia. GEGENBAUR 

 regards this as indicating a subordination of the functional importance of the 

 fibula in comparison with the tibia. 



7. The patella begins to ossify in the third year. 



8. To the metatarsals and the phalanges of the toes applies in general all 

 that has been said about the corresponding parts of the hand. 



(c) Development of the Joints. 



Inasmuch as the separate pieces of cartilage in the body are 

 formed by histological differentiation in the connective-tissue layers, 

 they are at first united to one another by remnants of the parent 

 tissue. This generally acquires a more compact fibrous condition 

 and is converted into a special ligament. 



Such a union of the separate skeletal elements is the prevailing 

 method in the lower Vertebrates, as, e.g., in the Sharks. In the" 

 higher Vertebrates, including Man, it is retained in many, but not 

 all, places, as, e.g., in the vertebral column, where the bodies of the 

 vertebrse are joined to each other by inter vertebral discs of con- 

 nective tissue. But at the places where the apposed skeletal parts 

 acquire greater freedom of motion upon each other, there appears, 

 in place of the simpler connective-tissue union, the more complicated 

 articular connection. 



