THE TRACHEA. 1837 



trachea, the left one being the first to reach this position. The inferior laryngeal 

 artery and veins are near them. The relations of the artery and nerve are given 

 with the relations of the thyroid. The remains of the thymus lie in front of the 

 trachea within the thorax. Owing to the forward inclination of the sternum, the 

 trachea is more deeply placed as it descends. A lymph-node or, more frequently, a 

 group of them is constantly found under the bifurcation. Tillaux l found the dis- 

 tance of the cricoid cartilage above the sternum (in a small series) to range in the 

 male from 4.58.5 cm., with an average of 6.5 cm.; and in the female from 5-7.5 

 cm., with an average of 6.4 cm. This distance, however, may be modified by other 

 factors than the length of the trachea. 



Growth and Subsequent Changes. In the infant the trachea measures 

 from 4-5 cm. in length, begins at a higher point in the neck, as has been shown for 

 the larynx, and divides at a higher point in the thorax. The level of this division 

 varies very much in the foetus, but at birth is generally opposite the third thoracic 

 vertebra. The lowest position is opposite the fourth and the range extends over 

 two vertebrae. 



There are comparatively few records of the changes during childhood. 2 We have found 

 it opposite the lower part of the fourth thoracic vertebra in a child whose age was estimated at 

 about three. Symington 3 has found it at the top of the fifth in two children of six and oppo- 

 site the fourth in one of thirteen. In the young adult it is opposite the disk between the 

 fourth and fifth thoracic vertebrae, which is its normal position, although it is not abnormal for 

 it to be opposite the fifth. Late in life it descends to the lower border of the fifth and even to 

 the seventh vertebra. 4 The trachea of the infant appears almost round, the rings forming a 

 relatively larger part, perhaps five-sixths of the periphery. According to several authorities, 

 the transverse diameter much exceeds the sagittal ; but, although we have seen this condition, 

 we are not inclined to agree that it is normal in the infant, unless, perhaps, at the lower end. 

 The size of the transverse section of the trachea is, for many reasons, hard to determine. 

 Merkel 5 thinks we may accept the following statement of the diameter of the upper part of the 

 trachea without fear of being much out of the way in particular instances : from six to eighteen 

 months, 5 mm. ; from two to three years, 6 mm. ; from four to five, 7 mm. ; from five to ten, 

 8 mm.; from ten to fifteen, jo-ii mm. Ossification of the rings begins decidedly later than in 

 the larynx. The earliest appearances of it observed by Chievitz were at about forty in man and 

 about sixty in woman. His youngest case of complete ossification was at fifty in man and 

 seventy-eight in woman. The deposit is first seen in the upper rings, but not in the first one, 

 the points being irregularly distributed along the borders. They come next in the lower rings, 

 and here at the posterior ends. As the process spreads, there is left a median unossified tract 

 along the trachea, which probably is usually invaded from below. 



THE BIFURCATION OF THE TRACHEA AND THE ROOTS OF 



THE LUNGS. 



The carina trachea (Fig. 1561) is a prominent semilunar ridge running antero- 

 posteriorly across the bottom of the trachea between the origin of the two bronchi. It 

 usually starts from a larger anterior triangular space and ends at a smaller pos- 

 terior one. Heller and v. Schrotter 6 found the framework of the spur cartilaginous 

 in 56 per cent., membranous in 33 per cent., and mixed in n per cent. The 

 spur, when cartilaginous, is derived in various ways : from a tracheal ring, from the 

 first ring of either bronchus, or from a combination of these sources. The height 

 of this ridge, especially when membranous, is difficult to measure, but these authors 

 believe that it may reach 6 mm. According to Luschka, the free edge of the spur 

 is 15 mm. from the apparent lowest point of the windpipe, seen from without. This 

 great distance should in part be accounted for by the interbronchial ligament, a col- 

 lection of fibres running transversely in the angle between the bronchi. This band is, 

 however, very variable in development and not constant, so that Luschka' s estimate 

 of the distance is probably excessive for most cases. Heller and v. Schrotter found 



1 Anatomic Topographique, 3me e'dit., 1882. 



2 Dwight : Frozen Sections of a Child, 1881. 



3 Anatomy of the Child, 1887. 



4 Mehnert : Ueber topographische Altersveranderungen des Atmungsapparates, 1901. 

 6 Handbuch der Topograph. Anat., Bd. ii., 1899. 



6 Denkschrift der Acad. Vienna, 1897. 



