26 Development of the Limbs^, Body-wall and Back in Man 



In Fig. D the separation of dorsal from ventro-lateral musculature is 

 clearly shown. The dorsal musculature is shown divided into three 

 columns in the upper thoracic region; caudally differentiation is not so 

 extensive. The musculature of the external oblique may be seen, in 

 Fig. D, covering the external intercostal muscle, the ribs and in part 

 the rectus musculature. In Fig. E the rectus musculature, internal 

 intercostal and internal oblique may be seen. Differentiation, however, 

 is not so far advanced at the stage shown in Figs. D and E as it is at the 

 stage shown in Fig. 34. The ventro-lateral abdominal musculature of 

 Embryo CTX is connected by an irregular dense band of tissue Avith the 

 pubic process of the anlage of the pelvic bone. This band of tissue is 

 represented with diagrammatic distinctness in the draAvings. 



The neural apparatus has undergone rapid development. Fig. 21 

 shows clearly the main branches arising from the typal thoracic nerve. 

 Muscle twigs are arising. The general appearance of the spinal nerves 

 at this stage is shown in Fig. E. 



The mesenchyme is extensive in amount. The blood-vessels are 

 similar in general distribution to those described in Embryo CLXIII, 

 but the vascular plexus is more extensively developed. 



In the posterior limb the central skeletal mass has assumed somewhat 

 definite outlines. Fairly good views of it are presented in Figs. D and E. 

 The pelvic portion of the skeleton of the limb consists of a central 

 region continuous with the head of the femur. From this central ace- 

 tabular portion spring iliac, ischial and pubic processes. The femur 

 is short and thick. It is indistinctly shown in Fig. D. The tibia and 

 fibula are of fairly definite form (Figs. D and E). The skeleton of the 

 foot has the form shown in Figs. D and E. It is composed of condensed 

 mesenchyme. No accurate division into parts can be distinguished. 



The main nerve trunks have continued their growth into the limb. 

 From them many of the principal muscular and cutaneous branches 

 have sprung. The general distribution of the lateral nerves of the limb, 

 the femoral and peroneal, and their branches, may be seen in Fig. D. 

 That of the median nerves of the limb, the obturator and tibial, in Fig. 

 E, In both figures the anterior border nerves (the ilio-hypogastric and 

 genito-crural) and the posterior border nerves (the pudic and posterior- 

 cutaneous) are shown. 



About the main branches of the nerves of the limb a differentiation 

 of musculature has begun. This is indicated in Figs. D and E. In Fig. 

 25 are shown the appearances in cross-section presented by the early 

 developing musculature of the leg. The blood-vessels of the limb are 

 shown in Figs. D and E. The sciatic artery is still the chief source of 



