120 REPORT— 1869. 



1. The various systems of tlie body are, in at least all the more symmetrical 

 animal forms, arranged in more or less perfect circles round the digestive tube. 



2. The visceral or costal arches of the vertebrate skeleton constitute, when fully 

 developed, circles external to those of the vascular system, and internal to the 

 primary stratum of the muscular system, and each visceral arch is a part of a 

 single segment of the body. 



.3. The limbs consist each of a girdle or limb-arch, and a radiation or appendage. 



That the limb-arch is not a radiation is sufficiently evident from its circling 

 always more or less round the body, and being sometimes complete above, some- 

 time complete below. 



4. Neither the limb-arch nor its appendage is the property of one particular seg- 

 ment. They receive nerves from various segments, not a very definite number, 

 and are very variable in position, especially the hind limb. 



5. Probably the typical position of the limb-girdle is superficial to the primary 

 muscular layer, as in the pectoral girdle of most animals, but it varies in position, and 

 this is explained by the development. The appendage is developed before the limb- 

 arch, and is an extension outwards of the ventral plate, while as yet that plate may 

 be considered as forming the periphery of the embryo ; and the arch is developed in 

 connexion with the appendage, while as yet the dorsal plates extend little outwards. 



6. The suspensorium and lower jaw form an arch corresponding with the limb- 

 arches ; and the opercular apparatus of fishes consists of appendages attached to it. 



In proof of this it may be mentioned that, 



a. The jaw is external to the visceral arc^hes of the skull. 



b. The jaw is composed of parts more complex than a visceral arch. 



c. The suspensorium, quadrate bone, or incus, is usually connected with at 

 least two segments of the skull. 



7. The difficulty of distinguishing the jaw as a limb-arch arises from the thin- 

 ness of the visceral walls in the cephalic and cervical regions. Hence the intimate 

 connexion between jaw and hyoid arch in fishes, and the connexion of the hyoid 

 bone in turn with the branchial arches, which are splanchnic. 



8. The three limb-arches may be considered as corresponding with the three 

 greatregionsof the body, viz. the cephalic, the cervico-thoracic, and the abdomino- 

 pelvic regions, which are respectively the seats of greatest development of the 

 animal, vascular, and vegetative systems. 



The crowding forwards of the limbs in many osseous fishes is in harmony with 

 the whole piscine structure, the great regions in fishes being comparatively undif- 

 ferentiated and crowded under the head, while the mass of the animal is a mere tail. 



The Human Mesocolon iUustrated hy that of the Womhat. 

 By Professor Cleland, M.D. 



The general an-angement of the small and gi'eat intestines in the Wombat is 

 very similar to what is found in the human subject, although they are of greater 

 proportional length. The paper pointed out that the arrangement of the perito- 

 neum in the Wombat exactly corresponded with the conditions which the writer 

 described in the ' Journal of Anatomy and Physiology,' May 18G8, as existing in 

 the human fcetus of three months. The descending, and half of the transverse 

 colon are provided, as in the human foetus, with a mesocolon springing from near 

 the middle line ; and the right half of the transverse colon, having crossed the 

 third part of the duodenum, is bound to the commencement of that part of the 

 intestine, near the pylorus, by a narrow fold of peritoneum, immediately above the 

 upper end of the mesocolon just mentioned. That narrow peritoneal fold marks 

 the neck of the primary loop of the intestine which formerly extended out at the 

 umbilicus, and the crossing of the duodenum by the colon is efiected by the twist 

 which tlie loop takes to the right. The mesocolon has no connexion ■\\-ith the I 

 pendulous mesogasti'ium or so-called great omentum. The position which the 

 writer lays down with regard to the human subject is, that while the left half of j 

 the transverse colon, together with the descending colon, has originally a meso- 

 colon, and is distinct from the mesogastrium, the right half of the transverse colon 

 has no mesocolon. 



