4 Go ELEMENTARY ANATOMY. 



colon to the stomach and duodenum, thus early initiated, 

 persists with great constancy. Each of the two ends of the 

 alimentary canal becomes perforated by means of a depres- 

 sion which appears on its surface, and which deepens till it 

 opens into the nascent alimentary canal. 



The large intestine is at first of less capacity than the 

 small, and the vermiform appendix is at first as wide as the 

 caecum. 



Immediately below the dilatation for the stomach a very 

 small offshoot grows out from the alimentary canal, and 

 around this a s:>ft mass of tissue is developed the future 

 liver. T.he transitions which take place with regard to the 

 blood-vessels in connexion with this part have been already 

 described in Lesson X. The part of the alimentary canal 

 which is pre-axial to the stomach becomes, of course, the 

 (esophagus. It also gives off diverticula, but as these (after- 

 wards the lungs) are not directly related to the alimentary 

 system, they will be noticed in the succeeding and last Lesson. 



1 8. Thus a certain rough and general approximation to 

 the earlier conditions of the digestive system found in man 

 manifestly persists in lower Vertebrata ; in some Fishes the 

 alimentary canal being, as we have seen, of nearly uniform 

 width throughout its course, without even a dilatation to form 

 a distinct stomach. The liver in its earliest condition recalls its 

 permanent form in Amphioxus. As we ascend through the 

 Vertebrate series, we find in the highest class a greater com- 

 plication of definite, distinct, and mutually related parts, 

 although the ascent is by no means regular. Not in man do 

 we find the most complex stomach, but in the Sheep. Not 

 in him is the caecum at its maximum, but in the Indris and 

 some others before mentioned. Valvulae conniventes, indeed, 

 are a marked character of the small intestine of man, but 

 they are yet more marked in the Ornithorhynchus. The liver 

 may be much more complex than in him, but it may also be 

 more simple even in his own class. The tongue may be 

 much longer and more mobile ; it may also be much shorter 

 and less mobile, or may abort altogether. Salivary glands 

 may be completely absent ; they may, on the contrary, attain 

 a size and complexity to which those of man are far from at- 

 taining. The alimentary system, then, hardly agrees with the 

 nervous system in presenting marked and readily appreciable 

 characters, by which man's organization exhibits an evident 

 and unmistakable superiority, though a certain superiority 

 probably exists in the reciprocal co-ordination of its parts, 



