THE ASCENT OF MAN. 461 



dowu iu frout of the sacrum and coccyx corresponding to the caudal 

 artery of quadrupeds shows signs of a former more extensive distribu- 

 tion, as it ends in a curiously convoluted structure known as the coccy- 

 geal gland, containing vestiges of vascular and nervous tissues. Traces 

 of caudal muscles still remain, notably the ischio-coccygeiis, which iu 

 animals moves the tail sideways, and the anterior and posterior sacro- 

 coccygeus, for flexing and extending it. Occasionally the agitator caudm 

 is found as a muscular slip passing from the femur to the coccyx. These 

 muscles can not be of any value iu man, as the coccyx is practically 

 immovable. At the point where the end of the spine was i)rimarily 

 attached to the skin a dimple is formed by regressive growth, and here 

 the direction of the hairs also indicates that an organ has become 

 aborted. 



Another interesting condition connected with segmentation is the vary- 

 ing number of the ribs. Most mammals have more ribs than man, and 

 as we descend in the scale they continue to increase. A study of devel- 

 opment indicates that a rib is probably to be considered as an integral 

 portion of a vertebra. As the arch of a vertebra incloses the central 

 nervous system, so the ribs inclose the visceral system. If this be cor- 

 rect they ought to be found throughout as far as the body cavity extends. 

 This is really the case. They exist in the neck as the anterior bars of 

 the transverse processes, in the loins as the transverse or costal pro- 

 cesses themselves, in the sacrum welded together into what are known 

 as the lateral masses. A great number of considerations derived from 

 comparative anatomy, from embryology, and from variations found in 

 the adult, combine to support these conclusions. 



Nothing would seem less likely at first sight than that the capacious 

 expanded brain-case or skull with its complicated structure should be 

 composed of segmental i^ieces like the vertebrte; yet there is no doubt 

 that the poet Goethe was on the right track when he made that impor- 

 tant generalization. The details of the segmentation are very far from 

 being worked out, but a vast amount of evidence indicates that the 

 general conclusion is correct. 



Since the predominant necessity in the construction of the skull is to 

 afford a protection for the brain, we need not be surprised to find that 

 it is very greatly modified in man. Enormous labor has been bestowed 

 upon craniology in an attempt to separate definitely the races of men 

 as well as to connect them with the lower forms. The success iu estab- 

 lishing races has not been such as was anticipated. A constant inter- 

 giadiug of forms defies all attempts at a hard and fast classification. 

 We also see types that intergrade between anthropoids and man, and 

 find abundant evidence that the human skull was derived from a form 

 similar to that of still lower mammals. 



At first man's skull seems to be much simpler than the ty})ical form. 

 The bones are lewer and less complicated. But follow back the course 

 of development and we find the bones separating — the frontal into two 



