24 CLASSIFICATION 



stand on its hind-legs in the erect attitude commonly attributed to 

 it in illustrated books of fables and the like, and we shall see that 

 the anterior and posterior ends of the trunk become upper and 

 lower, while the ventral surface faces to the front, and the dorsal 

 surface faces, if one may so speak, to the back. A frog thus 

 disposed has a comic resemblance to a human being, and the 

 reason is clear — the erect attitude in both cases brings about the 

 same relative positions of ends and surfaces. 



Let us next examine the two pairs of limbs possessed by Man. 

 A very cursory inspection will show that they are divided into 

 similar regions, and this is best expressed in tabular form — 



Anterior or Fore Limbs. Posterior or Hind Limbs. 



1. Upper arm. i. Thigh. 



2. Forearm. 2. Lower leg. ' 



3. Hand. 3. Foot. 



(a) Wrist. (a) Ankle. 



{b) Palm region. {b) Sole region. 



(c) Thumb and four fingers. (c) Great-toe and tour others. 



STRUCTURE OF THE HUMAN BODY 



It was long ago pointed out by Huxley that the body, apart 

 from the limbs, may be looked upon as a double tube. When 

 halved longitudinally, and the internal organs removed, this can 

 be very clearly seen (fig. 3), and the same thing is obvious in 

 the similarly divided carcasses of sheep and other animals to be 

 seen hanging up in a butcher's shop. The two tubes may also 

 be clearly seen in a cross section. One of them is dorsal, the 

 other ventral. The latter forms in the trunk the large cavity 

 of the chest and abdomen, being divided into two parts corre- 

 sponding to these two regions by a partition, the mid-riff or 

 diaphragm, which is partly fleshy, pardy fibrous. The thoracic 

 part contains the heart, lungs, most of the gullet, and part of 

 the large blood-vessels; while the abdominal part contains the 

 bulk of the digestive organs, the kidneys, and various other struc- 

 tures. The dorsal tube in the trunk is comparatively small, and 

 consists of a narrow canal running down within the backbone and 

 enclosing the spinal marrow. It is continued through the neck, and 

 in the head expands greatly into the large cavity of the cranium or 

 brain-case, in which the brain is situated. The brain and spinal 



