<>88 A TEXTBOOK OF PHYSIOLOGY 



developed. The brain of the frog is seen in Fig. 413. In reptilia, 

 the brain is long and narrow, much increased in size. It begins to 



.show marked differentiation with the appearance of the neopallium 

 the higher cortex, or brain proper. 



In birds, the brain is broad and highly developed, the greatest 



development being in the sizs of the striate bodies (corpora striata). 

 The thalamus and optic lobes are also highly organized. 



FIG. 410. POSITION ASSUMED BY FROG AFTEK REMOVAL OF THE ENTIRE BRAIN: IT 

 LIES LIMP AND FLACCID. 



The function of the brain may be studied on the frog. If 

 the cerebral hemispheres be destroyed, preferably by forceps by 

 dissection, and the bleeding stopped by wax (Fig. 414), the frog, 

 when the shock has passed off, will exhibit spontaneous movements 

 such as swimming when placed in water, and turning over if placed on 

 its back. If the corpora striata and optic thalami be destroyed, the 

 shock is greater, but the animal on recovery can still jump, swim, 

 climb an inclined board, and maintain its equilibrium. If the cere- 

 bellum and medulla oblongata are destroyed, the power to maintain 

 equilibrium vanishes, and the respiratory movements of the nares and 

 of the floor of the mouth cease. The animal lies in a listless condition 

 {Fig. 416), but still shows co-ordinated movements when stimulated, 

 since the spinal cord is still intact. 



SECTION I 



THE MEDULLA OBLONGATA AND PONS VAROLII 



The Medulla Oblongata. The medulla oblongata may be regarded 

 .as the expanded upper end of the spinal cord; indeed, it is sometimes 

 termed uhe spinal bulb. In this region, the central canal gradually 

 becomes more superficial, and eventually opens out, to form part of 

 the fourth ventricle. On either side of the middle line posteriorly 

 there are seen, at the lower end of the medulla, prominences which 

 represent the terminations of the posterior columns of the cord. Each 

 postero-median column ends in a. prominence on either side of the 

 middle line, known as funiculus gracilis, each postero-lateral in a 

 more laterally placed funiculus cuneatus. Prominent in the mid-line 

 anteriorly are the pyramids, which are composed of the pyramidal 

 fibres coming from the cortex, and have not yet crossed. The decus- 

 sation of these fibres takes place at the lower end of the medulla. 



