274 Dr. Waller on some Tissues of the Animal Frame, 



of siring, or by a couple of elastic bands, which I have found 

 more convenient. The animal's tongue may now be easily 

 discovered as described, and drawn out of the mouth with 

 a pair of tweezers. It will now be perceived (as I first ob- 

 served while dissecting one of these animals) that this organ 

 possesses an extraordinary degree of elasticity, and that with 

 care it may be extended in all directions until it is so attenu- 

 ated as to become nearly transparent. A few pins will enable 

 us to fix it over the opening made in the cork, where we can 

 examine it at our leisure. 



When the tongue is first extracted from the mouth it is 

 observed to be extremely pale, and the only vessels visible are 

 two veins with accompanying arteries, corresponding to the 

 lingual arteries in man, which, after ascending the throat in a 

 parallel direction, penetrate into the tongue, where they are 

 chiefly distributed at its inferior surface. In the substance of 

 the tongue they may be described in general terms as proceed- 

 ing by their main trunks towards the two tubercles, which are 

 found at its anterior extremity, and communicating in their 

 course by frequent anastomoses. After several minutes' ex- 

 posure they become more apparent from the general vascular 

 distention that takes place, and we observe the same pheno- 

 mena as when the conjunctiva is exposed to the contact of 

 some foreign substance. Thus the vessels become more dis- 

 tended and apparently increased in number, at the same time 

 they appear to terminate in the tissue of the organ, like the 

 minute fibres of roots. 



This vascular engorgement appears to arise in the first 

 instance entirely from the vital irritability of the organ, as it 

 is seen to commence as soon as the tongue is seized by the 

 tweezers, even before it is extracted from the mouth. After its 

 preparation this injection is further increased by the impedi* 

 ments which exist to free respiration and muscular action. The 

 peculiar manner in which this animal, devoid of ribs, breathes, 

 is well known. The number of respirations in a minute depends 

 much upon the external temperature, and varies from four to 

 thirty. The pulsations of the heart in the same period are 

 about sixty, which we may ascertain by observing the skin 

 over the heart as it rises at each contraction. Acquaintance 

 with these facts will be found useful in the subsequent inquiry. 

 Nervous trunks, in colour of a shining white, are found ac- 

 companying the vessels, and are best seen when the extended 

 tongue is viewed between the light. 



On the upper or papillary surface the eye detects minute 

 elevations above the rest of the membranes, which very much 

 resemble the granulations often existing on the inner surface 



