1096 



THYMUS GLAND. 



all the cavities (fig. 731.)- The lobular ca- 

 vities were completely filled by aggregations 

 of celloid particles, which were not manifestly 

 nucleated, nor provided with an envelope, but 



consisted chiefly of aggregations of oil drops 

 and molecules. Within the thorax at its 

 upper part there was a similar lobulated grey- 

 ish white mass, resting upon the lower part of 



Fig. 731. 



Convexity of lobe from oil gland of Sat. A homogeneous membrane encloses a multitude of celloid par- 

 ticles, the exterior row of which alone is visible, the rest of the mass being quite opaque. 



the trachea and the great vessels, and ex- 

 tending round so as to come in contact on 

 each side with the lung ; the structure of this 

 was precisely the same as that of the masses 

 at the root of the neck, with which however it 

 was not continuous. I am much inclined to 

 regard these organs as representatives of the 

 thymus, both from their structure and situa- 

 tion, and because I know not what else they 

 could be ; they are not for a moment to be 

 confounded with the ordinary adipose tissue. 



Among Insec/ivora the thymus forms two 

 nearly equal lobes, lying on the base of the 

 heart and origin of the large vessels, with 

 greater vertical than transverse dimensions. 

 In some individuals, at least, it is not persistent 

 throughout life, nor does it appear to be spe- 

 cially developed. 



In two Hedgehogs which I dissected, one 

 of which had been in a state of torpor until 

 three days before death, and the other had 

 been active and wakeful for several weeks, 

 I found at either side of the root of the 

 neck two roundish masses almost precisely 

 similar in appearance to those existing in 

 the same situation in the bat, and also two 

 broader and thinner ones lying in the ax- 

 illa? ; but there was no trace of any such 

 tissue in the thorax. The celloid particles 

 were more loaded with oil than in the bat, 

 especially in the dormant one, and in some 

 parts they were more or less broken up and 

 the oily matter diffused in the cavity. Re- 

 specting the existence of a real thymus 

 distinct from these glandular masses I am in 

 doubt, it is not altogether easy to distinguish 

 the structure from that of lymphatic glands 

 several of which lie upon the great vessels at 

 their origin from the heart. However this be 

 it is well worth remarking, that in two hi- 

 bernating animals belonging to different orders, 

 peculiar organs of precisely similar structure 

 were found ; while, on the other hand, in a 

 mole (an animal which I believe does not 

 hibernate) I could find no unequivocal trace 

 of thymus, nor of the peculiar oil glands which 

 I have described as existing in the bat and 

 hedgehog. This would indicate the existence 

 of the oil gland to have reference to hiberna- 

 tion, but a more extended inquiry on this 

 head is of course necessary before this sug- 

 gestion could have much claim to be received. 



Among Carnivora the thymus, except in 

 the cat tribe, where it seems generally to 

 vanish at an early period, is entirely thoracic, 

 resting upon the upper part of the pericar- 

 dium and the origin of the vessels. When 

 mature "it has considerable thickness and 

 substance in the direction from before back- 

 ward, and its right and left lobes irregularly 

 overlap each other, so as to render the sepa- 

 ration between them indistinct." When the 

 gland becomes attenuated it assumes the 

 form of a triangle, with the apex much pro- 

 longed upwards. 



The thymus has been found by Mr. 

 Simon in (young) seals, though other ana- 

 tomists, including Meckel, who, as he says, 

 was little likely to overlook its presence, 

 had not observed its existence ; from this 

 he concludes that it declines and disappears 

 in this family, as in most other mammalia. 

 Its form in the common seal, when pre- 

 sent, is nearly symmetrical, consisting of 

 two broad thickish lobes, which prolong 

 themselves upwards to the root of the neck, 

 and abruptly terminate by clubbed extremi- 

 ties, which are deeply grooved in front by the 

 left vena innominata. 



In the order of Marsupialia, three most 

 eminent anatomists had failed to recognise 

 the existence of a thymus, Mr. Simon has, 

 however, discovered this gland in several in- 

 stances, it is mostly placed on the pericar- 

 dium, not reaching into the neck. In the 

 foetus of the Kangaroo it has a peculiar con- 

 formation, being provided with a third, me- 

 dian, lobe projecting outwards between the 

 two others. 



Among Rodents the thymus differs in 

 shape in the various genera. It consists in the 

 rat of two elongated parallel lobes, reaching 

 from the base of the heart to the root of the 

 neck, In the hare it is much thicker, but still 

 only extends to the root of the neck. In the 

 hibernating rodents the thymus is believed 

 to undergo at the approach of winter a re- 

 markable alteration, apparently as a prepara- 

 tion for the long sleep of that season. Tie- 

 demann describes in a Marmot, which he 

 examined in the month of November while 

 in a state of torpor, the gland as " filling the 

 whole of the anterior and posterior medias- 

 tina, extending along the great vessels of the 



