Natural History of Cottonmouth Moccasin, Agkistrodon piscovorus (Reptilia). Ray D. Burkett
depending upon the position on the body. Scales on the neck are considerably smaller than those elsewhere on the body and are arranged in two or three more rows than those at mid-body. The skin in the region of the throat, neck, and fore-body is especially elastic and allows the swallowing of large prey. Posteriorly from the mid-body the scales decrease in size and become more angular, those on the tail tending to be rhomboidal and wider than long. In the region of the anus the number of scale rows diminishes rapidly, leaving only 12 to 14 rows at the base of the tail and only three rows immediately ahead of the tail tip. The tail ends in a spine composed of two scales: one scale covers the bottom, lower parts of the sides, and tip of the spine; and a shorter dorsal scale covers the top and upper parts of the sides of the basal two-thirds of the spine. The spine of embryos and young cottonmouths is blunt, but is pointed in most adults.
TABLE 3.—Variation in Numbers of Supralabials and Infralabials in a Brood
of Seven Cottonmouths.
| Number of individuals | Number of supralabials | Number of infralabials |
| 1 | 7 | 9 |
| 1 | 7 | 9-10 |
| 2 | 7-8 | 8-9 |
| 1 | 7-8 | 9 |
| 1 | 8 | 9-10 |
| 1 | 8-9 | 10 |
TABLE 4.—Analysis of Number of Scale Rows at Three Parts of the Body
in 81 Cottonmouths.
| Number of scales per row | Neck | Mid-body | Anterior to anus | |||
| Number of individuals | Percentage | Number of individuals | Percentage | Number of individuals | Percentage | |
| 29 | 1 | 1.2 | ||||
| 28 | 3 | 3.7 | ||||
| 27 | 52 | 64.2 | ||||
| 26 | 16 | 18.0 | 2 | 2.5 | ||
| 25 | 8 | 9.9 | 67 | 82.7 | ||
| 24 | 1 | 1.2 | 4 | 4.9 | ||
| 23 | 8 | 9.9 | 4 | 4.9 | ||
| 22 | 4 | 4.9 | ||||
| 21 | 68 | 84.0 | ||||
| 20 | 5 | 6.2 | ||||
The number of scale rows on the neck, at mid-body, and just anterior to the anus is relatively constant at 27-25-21, respectively; but some individual variation is evident (Table 4). Since the rows are diagonally arranged, it is necessary in counting scales to proceed either anteriorly or posteriorly across the back; or the row may be counted in either direction up to the center of the back and then reversed on the other side of the snake. In order to count the scale rows in a position where no scale reduction or addition was occurring and to avoid as much error as possible, I counted from anterior to center and back on the neck, in any direction at mid-body, and from posterior to center and back near the anus. Because females generally are the larger in circumference posteriorly, they could have more scale rows than males just anterior to the anus. The few snakes having more than 21 scale rows in the posterior region offer no conclusive evidence as to tendencies, but in both instances in which this occurred the females outnumbered the males three to one. An odd, rather than an even, number of scale rows occurs on most of the length of the snakes examined, because there is a mid-dorsal row and scale rows tend to be lost on both sides at about the same level. An example of scale reduction of one snake was as follows:
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