AORTA. 



191 



kind, the number of branches is most fre- and superior mesenteric arise by a common 



quently increased to four, by the left vertebral trunk as in the tortoise; sometimes there are 



arising from the arch between the left carotid two or more renal arteries on one or both sides, 



and left subclavian, as in the phoca vitulina ; and sometimes the primitive iliacs are given 



next to this in frequency is the instance of the off much higher than usual, in which case they 



inferior thyroid arising from the arch between are sometimes connected by a cross branch 



the innominata and left carotid, then the in- before they divide into the external and in- 



ternal mammary, and, lastly, the most un- 

 usual is the thymic artery : it is more unusual 

 to find the number of branches coming from 

 the arch increased to four, in consequence of 

 the innominata being absent, the right carotid 

 and right subclavian arising separately ; in such 

 a distribution the right subclavian most fre- 

 quently arises from the left extremity of the 



ternal iliacs : it sometimes happens, when the 

 iliacs are given off higher than usual, that the 

 inferior mesenteric arises from the left of 

 them. 



The diseased conditions of the aorta are 

 described in the articles ARTERY and HEART. 

 The aorta, as Beclard remarks,* is more sub- 

 ject than any other artery to the ovoid dila- 



arch after the left subclavian ; it may, how- tation in its ascending, and the lateral dila- 

 ever, be the first branch of the arch to the right, tation in its descending portion ; it is also very 

 or it may arise between the two carotids, or, subject to osseous or calcareous deposits, to 



as more rarely happens, between the left 

 carotid and left subclavian. The number of 

 branches arising from the arch will be in- 

 creased to five or upwards, when two or more 

 of the above-mentioned anomalous branches 

 arise from it at the same time. Of the second 

 kind of anomaly, or that by diminution of the 

 number of branches, the most frequent is 

 where these are reduced to two, of which 

 there occur the following varieties : a. the in- 



fissures and ulcerations, to tubercles and small 

 abscesses in its parietes, and to aneurism. 

 Wounds of the aorta are constantly mortal. 

 Laennec has observed a particular lesion of 

 this vessel ; it was a fissure of the internal 

 and middle coats, from which the external tunic 

 was extensively separated by a quantity of 

 blood which had been effused between it and 

 the middle tunic. The late Mr. Shekelton has 

 described, in the Dublin Hospital Reports, 



nominata sometimes gives off the left carotid a form of aneurism of the lower part of the 



as an additional branch, and the left subcla- abdominal aorta, in which the blood forced its 



vian arises separately, as in many quadrumana, way through the internal and middle coats, 



several of the carnivora, as the lion, cat, dog, dissected the middle from the external for the 



weazel, several rodentia, &c. ; b. sometimes there space of four inches, and then burst into a lower 



are two arteriae innominatae, each dividing in part of the canal of the artery, forming a new 



a symmetrical manner into the subclavian and 



eventually superseded the 



channel which 



carotid of its own side, as in cheiroptera and old one, which the pressure of the tumour 

 the dolphin ; c. sometimes when the arch gives obliterated, 

 off but two trunks, one of them divides into 



the two carotids, and the other into the sub- 

 clavians; d. the right subclavian may arise 

 distinct, and a common trunk give off the two 

 carotids and left subclavian ; the origin of a 

 single trunk from the arch of the aorta sup- 

 plying the arteries of the head and upper 



Granular excrescences are sometimes formed 

 on the valves of the aorta, which Corvisart 

 conjectured to be of venereal origin. The in- 

 ternal tunic of the aorta sometimes presents a 

 red appearance, not peculiar, however, to this 

 vessel, and occurring in certain forms of fever. 



Obliteration or constriction of the aorta is a 



extremities is equivalent to a division of the condition rarely met with; its existence may 

 aorta into an ascending and descending trunk, be traced either to pressure on the vessel from 

 already noticed. The third kind of anomaly without, morbid thickening of its coats, or the 



partakes of the characters of the two pre- 

 ceding, although the number of branches is 

 the same as in the normal state : its varieties 

 are, a, the left vertebral arising from the arch, 

 whilst the left carotid comes from the inno- 



formatioa of coagula internally ; this latter 

 occurrence being most usually a consequence 

 of the spontaneous cure of aneurism. 



Aneurisms of the aorta produce various 

 effects on surrounding parts ; thus the heart, 



minata; 6, the two carotids may arise from a lungs, trachea, oesophagus, pulmonary artery, 

 common trunk between the origins of the right large veins, thoracic duct, and the various 

 and left subclavians, as in the elephant ; c, organs in the abdomen placed in their vicinity, 



may suffer derangement of their functions, 

 displacement, atrophy or partial destruction, 



/ j^ * / 



the right subclavian and right carotid may 



according to the degree of pressure to which 



arise as distinct branches, whilst the left carotid 

 and left subclavian come from a common 



trunk, forming a complete inversion of the they are subjected, 



usual order ; d, the left carotid may arise from Aneurisms occurring in the ascending por- 



the innominata, whilst the right carotid comes tion of the aorta, which is within the pericar- 



from the part of the arch in the situation usu- dium, are often attended during life by many 



ally occupied by the origin of the left carotid, symptoms very similar to those of disease of the 



Anomalies of the branches of the descending heart itself, while their pressure may produce 



aorta are less. frequent; the following are among a diminution of the calibre of the pulmonary 



the more remarkable : a, the cceliac and dia- artery, obstruct the free passage of the blood 



phragmatic may arise above the diaphragm ; through the vena cava superior, and even in- 

 one or both of the diaphragmatics may be 



given off by the cceliac ; sometimes the cceliac * Dictionnaire de Mcdecine, art. Aorte. 



