Chap. I. Rudiments. 23 



mentary condition, for they consist, with the exception of the 

 basal one, of the centrum alone. 53 They are furnished with 

 some small muscles ; one of which, as I am informed by Prof. 

 Turner, has been expressly described by Theile as a rudimentary 

 repetition of the extensor of the tail, a muscle which is bo 

 largely developed in many mammals. 



The spinal cord in man extends only as far downwards as the 

 last dorsal or first lumbar vertebra; but a thread-like struc- 

 ture (the filum terminalt) runs down the axis of the sacral part 

 of the spinal canal, and even along the back of the coccygeal 

 bones. The upper part of this filament, as Prof. Turnei 

 informs me, is undoubtedly homologous with the spinal cord t 

 but the lower part apparently consists merely of the pia mater, 

 or vascular investing membrane. Even in this case the os 

 coccyx may be said to possess a vestige of so important a 

 structure as the spinal cord, though no longer enclosed within 

 a bony canal. The following fact, for which I am also in- 

 debted to Prof. Turner, shews how closely the os coccyx corre- 

 sponds with the true tail in the lower animals : Luschka has 

 recently discovered at the extremity of the coccygeal bones a 

 very peculiar convoluted body, which is continuous with the 

 middle sacral artery ; and this discovery led Krause and Meyer 

 to examine the tail of a monkey (Macacus), and of a cat, in both 

 of which they found a similarly convoluted body, though not at 

 the extremity. 



The reproductive system offers various rudimentary struc- 

 tures; but these differ in one important respect from the 

 foregoing cases. Here we are not concerned with the vestige of 

 a part which does not belong to the species in an efficient state, 

 but with a part efficient in the one sex, and represented in the 

 other by a mere rudiment. Nevertheless, the occurrence of 

 such rudiments is as difficult to explain, on the belief of the 

 separate creation of each species, as in the foregoing cases. 

 Hereafter I shall have to recur to these rudiments, and shall 

 shew that their presence generally depends merely on inheri- 

 tance, that is, on parts acquired by one sex having been 

 partially transmitted to the other. I will in this place only give 

 some instances of such rudiments. It is well known that in the 

 males of all mammals, including man, rudimentary mammsB 

 exist. These in several instances have become veil developed, 

 and have yielded a copious supply of milk. Their essential 

 identity in the two sexes is likewise shewn by their occasional 

 sympathetic enlargement in both during an attack of the 



M Owen, ' On tho Nature of Limbs,' 1S49, p. 114. 



