Mr. Mayo on Human Physiology. 99 



"Another remarkable circumstance concurs with the 

 preceding, in establishing a resemblance between the action 

 of the iris and that of the voluntary muscles. The iris re- 

 ceives nerves from two sources, from the sentient part of 

 the fifth, and from the third : the main part of the latter is 

 distributed as a voluntary nerve to the muscles of the eye. 

 Now, if the head of a pigeon be cut off, and instantly 

 after the upper part of tne cranium be removed, and the 

 entire brain be taken out, on pinching the portion of the 

 third nerve, which remains attached to the eye, the iris acts 

 suddenly, just as the biceps flexor cubiti acts in an animal 

 recently killed, when the nerve which supplies that muscle 

 is pinched. A similar injury produced no visible effect. 



'' If, again, the third nerve be divided in the cranial ca- 

 vity, while the animal is alive, the pupil immediately dilates 

 to the utmost, and remains immoveable, the ins being 

 seemingly paralyzed." 



We shall pass over the account of the voluntary move- 

 ments of the body, to conclude our short notice of Mr. 

 Mayo's work, with the following extract upon the subject 

 of the reparation of broken or divided parts. 



" When a considerable portion of skin is removed, the 

 cellular membrane inflames below the blood, which stiffens 

 on the raw surface, and secretes pus, and forms a crop of gra- 

 nulations; these gradually rise to the level of, and higher 

 than the surrounding skin ; the secreting surface appears to 

 diminish daily, and becomes in patches, or, at its edges, con- 

 verted into a tender whitish substance, which thickening be- 

 comes opake, and forms a cicatrix : on the day that a portion 

 of a cicatrix is completed, it is insensible ; about a fortnight 

 afterwards it feels as if pricked with a needle. 



" Thus in the formation of a cicatrix after destruction of the 

 skin, the new material is produced, not by the neighbouring 

 cutis, but by a growth from the subcutaneous texture. 



** When tendons, or nerves, cartilages, or bones, are di- 

 vided or broken across, the process of their reunion does not 

 resemble the adhesion of divided skin, but has more in com- 

 mon with the growth of a cicatrix. The disjoined surfaces 

 do not cohere immediately, but through the intervention of 

 a third substance, which appears produced from the neigh- 

 bouring cellular texture. 



*' If the tendo achillis be examined in a dog forty-eight 

 hours after division, upon removing the skin, the subjacent 

 cellular membrane, which surrounds the tendon, appears 

 loaded with coagulable lymph and extravasated blood. 



H 2 



