From the above description it is evident that the coverings of the innominata may be ar ranged into ten layers, which, enumerated from the surface, consist of 1. The skin. 2. Layer of superficial fascia. 3. Platisma myoides muscle. 4. Superficial fascia. 5. First bone of the sternum, sternal ex tremity of the right clavicle, sterno-mastoid muscle, with its accompanying vein the steno and inter-clavicular ligaments and anterior layer of deep cervical fascia. 6. Cellular tissue, fat, containing large vein and a gland ; the second layer of deep cervical fascia. 7. Stemo-hyoid muscle. 8. Sterno-thyroid muscle. 9. Third layer of deep cervical fascia. 10. Cellular tissue containing the first cardiac nerve, right inferior thyroid, and left brachio-cephalic veins, glands, tkc.
Arrived opposite to the right stemo-clavicu lar articulation and to the interval between the sternal and clavicular insertions of the stemo mastoid muscle, the arteria innominata usually divides into the right carotid and subclavian arteries. It rarely gives off any branches ante cedent to its division, but a small third branch is frequently observed proceeding from it to distribute itself in front of the trachea, and ter minate in the thyroid gland. Mr. Harrison, in his work on the Surgical Anatomy of the Arteries, has named it the " middle thyroid artery." The French anatomists give M. Neubauer the credit of discovering it, and consequently term farterc thyroidienne de Neubauer " It is, however, as frequently given off from the aorta between the artcria iuno minata and left carotid.
When we consider the relation which the in nominata bears to the important organs sur rounding it, we can scarcely be at any loss to account for the apparently remote symptoms present in aneurism of this vessel ; such, for instance, as cedema and blueness of the upper extremities, head and neck, cough, difficulty of breathing and swallowing, vertigo, failure of sight, &e. Where the tumor extends to wards the right side it presses upon the right brachio-cephalic vein, preventing the return of blood from the right arm and side of the head and neck ; if upwards in that direction the carotid and subclavian arteries become im plicated, and consequent interruption to the circulation ensues; if forwards, the passage of blood is stopped through the left braehio ceplialie vein and the inferior thyroid venous plexus; if to the left, it encroaches upon the left carotid artery and trachea, whilst by en larging backwards it acts immediately upon the trachea and mediately upon the esophagus. Although the above facts are interesting, as serving to elucidate the various phenomena occurring in this malady, I fear that we must not attach too much importance to them as means of diagnosis, inasmuch as many, if not all, of the above symptoms may result from enlargement of other vessels and other causes, indeed we have only to turn to the admirable work of Mr. Allan Burns on the Surgical Ana
tomy of the head and Neck, to be at once aware of the probability of deception in this respect. Anomalies.—There are perhaps few arteries in the body which present so many varieties and anomalies as the innominata, whether stu died with respect to its extent, course, situ ation, or the number of branches which it gives off. In the first place, it is frequently met with extending up into the neck as high as the thyroid cartilage before it divides into its ultimate branches, and sometimes lying in front of the trachea. It is scarcely necessary to remark in how great a degree this anomaly increases the difficulties and dangers attending the operation of tracheotomy. Secondly, the most remarkable variety occurring in the eourse of this artery is described by M. Velpeau, who, in his Elftens de Medeeine Operatoire, men tions three instances in which it passed to the left side in front of the trachea, and subse quently wound from before backwards over this organ, returning between the oesophagus and vertebral column, to its usual points of division opposite the right sterno-clavicular articulation. Thirdly, the innominata is also occasionally irregular as to situation. It has been found arising from the centre of the trans verse portion of the arch of the aorta instead of its commencement, and dividing into right and left carotid arteries, the right subelavian taking its origin from the spot usually occupied by the innominata. Again, instead of being placed on the right it has been met with given off from the left or posterior part of the arch dividing into the right and left earotids and left subelavian, in other instances into left sub clavian and left carotid. Cases are also on record in which the innominata was altogether absent, the right carotid and subelavian arte ries arising directly from the arch of the aorta. Fourthly, it is frequently anomalous in the Humber of branches it gives off. Occasionally the left carotid arises from it in addition to its usual branches, sometimes it divides into the two carotids instead of the subclavian and carotid ; and Tiedentann mentions an instance where it gave off the right internal mam mary.